That might be true in English Grammar 101 but NOT Geek Grammar 101.
Have you ever actually read a Greek grammar?
What you are promoting is a lexical fallacy know as the "root fallacy"
Root fallacy: assigning the (supposed) original meaning of a word to its usages throughout history;
Lexical Fallacies by Linguists
See e.g.
…..Some people claim that “aion/aionios” cannot mean eternity/eternal because they sometimes refer to things which are not eternal.
But neither word is ever defined/described, by other adjectives or adjectival phrases, as meaning a period of time less than eternal, in the New Testament, as in the following verses.
…..In 9 of these verses Jesus has defined “aionios” as eternal. Jesus used “aionios” twenty nine times. He never used “aionios to refer to anything that was clearly not eternal.
In 10 verses Paul has defined “aionios” as eternal.
In twenty four [24] of the following verses aion and aionios are defined/described as eternal, everlasting, eternity etc, by comparison or contrast with other adjectives or adjectival phrases.
[1] Romans 1:20
(20) For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal [aidios] power and Godhead; so that they are without excuse:
[2] Romans 16:26
(26) But now is made manifest, and by the scriptures of the prophets, according to the commandment of the everlasting [aionios] God, made known to all nations for the obedience of faith:
In Rom 1:20 Paul refers to God’s power and Godhead as “aidios.” Scholars agree “aidios” unquestionably means eternal, everlasting, unending etc. In Rom 16:26, Paul, the same writer, in the same writing, refers to God as “aionios.” Paul has used “aidios” synonymous with “aionios.” In this verse by definition “aionios” means eternal, everlasting.
[3] Luke 1:33
(33) And he shall reign [basileusei][Vb] over the house of Jacob for ever; [aionas] and of his kingdom [basileias][Nn] there shall be no end.[telos]
In this verse the reign basileusei, which is the verb form of the word, is "aionas" and of the kingdom basileias, the noun form of the same word, "there shall be no end.” “Aionas” by definition here means eternal.
[4] 2 Corinthians 4:17-18
(17) For our light affliction, which is but for a moment, worketh for us a far more exceeding and eternal [aionios] weight of glory;
(18) While we look not at the things which are seen, but at the things which are not seen: for the things which are seen are temporal;[proskairos] but the things which are not seen are eternal [aionios]
In this passage “aionios” is contrasted with “for a moment,” vs. 4, and “temporal,” vs. 5. “Age(s)” an indeterminate finite period, it is not the opposite of “for a moment”/”temporal/temporary” “eternal” is. “Aionios” by definition here means “eternal.”
[5] 2 Corinthians 5:1
(1) For we know that if our earthly house of this tabernacle were dissolved, we have a building of God, an house not made with hands, eternal [aionios] in the heavens.
In this verse “aionios house” is contrasted with “earthly house which is destroyed.” Is God going to replace our destroyed earthly house with a house which only lasts a little longer and will be destroyed at the end of an age? The aionios house is not destroyed, the opposite of “is destroyed.” Thus, “aionios” by definition here means “eternal.”
[6] Hebrews 7:24 but because Jesus lives forever [aion] he has an unchangeable [aparabatos] priesthood.
In this verse “aion” is paired with “unchangeable.” If “aion” means “age(s),” Jesus cannot continue “for a finite period” and be “unchangeable” at the same time. Thus “aion” by definition here means “eternal.”
[7]1 Peter 1:23
(23) For you have been born again, not of perishable seed, but of imperishable, [aphthartos] through the living and enduring word of God. …
1 Peter 1:25
(25) but the word of the Lord endures forever.[aion] " And this is the word that was preached to you.
In verse 23 “word of God” is paired with “imperishable.” The same writer, Peter, in the same writing 1 Peter in verse 25 writes the word of God “endures eis ton aiona/unto eternity. ” Thus by definition “aion” here means “eternity.”
[8]1 Timothy 6:16
(16) Who only hath immortality, [aphthartos] dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom be honour and power everlasting [/aionios]
In this verse “aionios” is paired with “immortality.” If “aionios” is only a finite period, God cannot be “immortal” and only exist for a finite period at the same time. Thus “aionios” by definition means “eternal.”
[9] Galatians 6:8
(8) For he that soweth to his flesh shall of the flesh reap corruption; [fthora] but he that soweth to the Spirit shall of the Spirit reap life everlasting. [aionios]
In this verse “aionios” is contrasted with “corruption.” “Fleshly” people reap “corruption” but spiritual people reap “life aionios,” i.e. “not corruption.” “Age(s), a finite period, is not opposite of “corruption.” Thus “aionios life” by definition here means “eternal/everlasting life.”
[10] John 6:58
(58) This is the bread that came down from heaven. Your ancestors ate manna and died, but whoever feeds on this bread will live forever.[aionios]
In this verse Jesus contrasts “aionios life” with “death.” If “live aionios” is only a finite period, a finite period is not opposite “death.” Thus “aionios” by definition here means “eternal.”
[11] John 10:28
(28) I give them eternal [aionios] life, and they shall never [aion] perish; no one will snatch them out of my hand.
In this verse Jesus pairs “aionios” and “aion” with “[not] snatch them out of my hand.” If “aion/aionios” means “age(s), a finite period,” that is not the opposite of “[not] snatch them out of my hand’” “Aionios life” by definition here means “eternal life.”
[12]1 John 2:17
(17) The world and its desires pass away, but whoever does the will of God lives forever. [aion]
In this verse “aionios” is contrasted with “pass away,” “lives aionios” cannot mean a finite period, which is is not opposite of “pass away.” Thus “lives aionios” by definition here means “lives eternally.”
[13]1 Peter 5:10
(10) And the God of all grace, who called you to his eternal [aionion] glory in Christ, after you have suffered a little while, [oligon] will himself restore you and make you strong, firm and steadfast.
In this verse “aionios” is contrasted with “little while” Does Jesus give His followers a finite period of glory then they eventually die? Thus “aionios” here, by definition, means “eternal.”
[14] Romans 2:7
(7) To those who by persistence in doing good seek glory, honor and immortality, [apftharsia] he will give eternal [aionios] life.
In this verse “aionios” is paired with “immortality.” If “aionios” is only a finite period, believers cannot seek for “a finite period,” and “immortality” at the same time. But they can seek for “eternal life” and “immortality” at the same time. Thus by definition “aionios life” here means “eternal life.”
[15] 1 Timothy 1:17.
(17) Now unto the King eternal, [aion] immortal, [aphthartos] invisible, the only wise God, be honour and glory for ever [aion] and ever [aionios]. Amen.
In this verse “aion” is paired with “immortal.” “Aion” cannot mean “age(s),” a finite period and immortal at the same time. Thus “aion” by definition here means “eternal.”
[16] Revelation 14:11
(11) And the smoke of their torment ascendeth up for ever and ever:[eis aionas aionon] and they have no rest day nor night, who worship the beast and his image, and whosoever receiveth the mark of his name.
In this verse “aionas aionon torment” is paired with “no rest day or night.” If “aionas, aionon” means “a finite period” at some time they would rest, “Aionas, aionon” by definition here means “forever and forever.”
[17] John 3:15
(15) That whosoever believeth in him should not perish, but have eternal [aionion] life.
In this verse Jesus pairs “aionion” with “shall not perish.” Believers could perish in a finite period, “aionion life” by definition here means eternal life.
[18] John 3:16
(16) For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting [aionion] life.
In this verse Jesus pairs “aionion” with “should not perish.” Believers could eventually perish in a finite period, thus by definition “aionion life” here means eternal or everlasting life.
[19] John 5:24
(24) Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting [aionios] life, and shall not come into condemnation; but is passed from death unto life.
In this verse Jesus pairs “aionios” with “shall not come into condemnation” and “passed from death unto life.” “Aionios” does not mean “a finite period,” by definition here it means “eternal,” unless Jesus lets His followers come into condemnation and pass into death.
[20] Romans 5:21
(21) That as sin hath reigned unto death, even so might grace reign through righteousness unto eternal [aionios] life by Jesus Christ our Lord.
In this verse “aionios life” is contrasted with death. “A finite period life” is not opposite death, “eternal life” is. “Aionios life” by definition here means ‘eternal life.”
[21] Ephesians 3:21
(21) to him be glory in the church and in Christ Jesus throughout all generations, for ever [tou aionios] and ever! [ton aionion] Amen.
In this verse “tou aionios ton aionion” is paired with “throughout all generations.” "Age(s)" a finite period cannot refer to "all generations." By definition “tou aionios ton aionion” means forever and ever.
[22] John 3:36 He that believeth on the Son hath everlasting [aionios] life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him.
In this verse aionios life is contrasted with “shall not see life.” If aionios means an indefinite age that is not opposite “shall not see life” By definition aionios means eternal.
[23] John 4:14 But whosoever drinketh of the water that I shall give him shall never thirst; but the water that I shall give him shall be in him a well of water springing up into everlasting [aionios] life.
In this verse aionios is contrasted with “shall never thirst.” If aionios means an indefinite age that is not opposite “shall never thirst.” By definition aionios means eternal.
[24] John 6:27
(27) Labour not for the meat which perisheth, but for that meat which endureth unto everlasting [aionios] life, which the Son of man shall give unto you: for him hath God the Father sealed.
In this verse “aionios meat” is contrasted with “meat that perishes” .” If aionios means an indefinite age that is not opposite “meat that perishes.” By definition aionios means eternal.
[25] John 8:51
(51) Very truly [amen amen] I tell you, whoever obeys my word will never [ou mé eis ton aiona] see death."