What does the greek word aionion mean? eternal or age-enduring or both. If aion means age, then how can its adjective mean anything but pertaining to the age. How can it mean eternal?
If you look up aion and aionios you will see that their meanings are heavily determined by context.
Eternal is a possible meaning of aionios, but not the only meaning.
If you want to make your head spin, look up the meanings of the preposition en in the lexicon.