The Scripture doesn’t say anything specific about celebrating birthdays. Because pagans celebrate birthdays, many people think doing so must be a pagan thing.
However, in the East during Biblical times, they did mark special anniversaries.
A Cohen began his service at 30 years of age, so we know they kept track of their age. Instead of the way we tend to do it nowadays, they would throw a big celebration and give gifts to others as thanksgiving to the Almighty.
It’s just like the thanksgiving offering at the Temple – you buy anything your heart desires and everyone gets to take part.
So, just because pagans do it doesn’t necessarily make it bad or wrong. Let us remember that every year when we celebrate Sukkot, we are celebrating the birthday of the Messiah!