Jehovah's Witnesses believe that celebrating anyone's birthday is a pagan custom based on false religious practices and superstition.
Jehovah's Witnesses do not believe in superstition or good luck. Isaiah 65:11,12.
They say that the only birthdays mentioned in the Bible were celebrated by two rulers who didn't worship Jehovah. Genesis 40:20 and Mark 6:21.
According to the Witnesses, birthdays were celebrated in honor of pagan Gods. They say that on May 24 the Romans celebrated the birthday of Diana, a pagan Goddess. On May 25 they celebrated the birth of Apollo, their sun god.
The Watchtower Magazine Nov 15, 2003, Questions From Readers re: birthstones says, 'Jehovah’s Witnesses do not celebrate birthdays. This is because such celebrations focus too much attention on the individual and the only birthdays of Bible record are those of pagan rulers who did not serve God. Genesis 40:20; Matthew 14:6-10.'
In the early 1900's, the Jehovah's Witnesses, then known as the Bible Students, did celebrate birthdays and Christmas. It was even customary to have Christmas dinner at their headquarters in New York. (See The Watchtower Magazine Oct 15, 1998, Questions From Readers re: why it's ok to celebrate a wedding anniversary and not a birthday anniversary.)