This is a question for those who believe everything has to come from the Bible: Why do you celebrate birthdays if those are also celebrated by pagan cultures and the few references to a birthday celebration are about heathens?
Hosea 7:5 Good News Translation (GNT)
5 On the day of the king's celebration they made the king and his officials drunk and foolish with wine.
Job 1 New International Version (NIV)
Prologue
1 In the land of Uz there lived a man whose name was Job. This man was blameless and upright; he feared God and shunned evil. 2 He had seven sons and three daughters, 3 and he owned seven thousand sheep, three thousand camels, five hundred yoke of oxen and five hundred donkeys, and had a large number of servants. He was the greatest man among all the people of the East.
4 His sons used to hold feasts in their homes on their birthdays, and they would invite their three sisters to eat and drink with them. 5 When a period of feasting had run its course, Job would make arrangements for them to be purified. Early in the morning he would sacrifice a burnt offering for each of them, thinking, “Perhaps my children have sinned and cursed God in their hearts.” This was Job’s regular custom.
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Biblical References.
A close study of the Biblical text shows that the Bible is not altogether wanting in references to the subject; for, while it lacks positive accounts, it contains passages from which it may be inferred that the custom of remembering birthday anniversaries was not wholly unknown among the Jews. "The day of our king" (Hosea vii. 5), on which the princes made the king sick with bottles of wine, and the king himself "stretched out his hand with scorners," alludes more probably to a birthday festival than to a solemn occasion, such as the anniversary of his installation, which would have been observed with more decorum (see Josephus, "Ant." xv. 9, § 6).
Birthdays might not have been celebrated by the common people with great solemnity, yet they did not pass wholly unnoticed, and were remembered by congratulations, as in modern times. Jeremiah not only cursed the day of his birth, but wished that it should not be blessed (Jer. xx. 14), as though such had been the custom.
It is said of Job, "and he cursed his day" (Job iii. 1). The emphatic and determining expression "his day" implies the idea that he, like everybody else, had a certain day of the year singled out for a certain purpose, which we learn further was the anniversary of his birth.
Weaning on Second Birthday.
The second or third birthday of a child whose coming into the world was very much desired by his parents was usually made the occasion of a feast, because the child was then weaned, and had consequently passed the dangerous and uncertain stage of infancy. Abraham made a great feast on the day Isaac was weaned (Gen. xxi. 8). This occurred, according to Rashi, at the expiration of twenty-four months. Bishop Ely ("Holy Bible Com."
l.c. on the passage) says: "By comparing I Sam. it would seem that this was very probably a religious feast." Hannah postponed the yearly family feast at Shiloh until she had weaned Samuel, in order to celebrate his birthday at the same time (I Sam. i. 23, 24). According to Rashi and Midr. R. Samuel,
l.c., this also occurred at the end of twenty-four months. Yet from II Chron. xxxi. 16 it may be inferred that Samuel was weaned at the end of his third year; for only from that age were children admitted to the service of the Temple."
BIRTHDAY - JewishEncyclopedia.com