Inactive users shouldn't get the 15 point birthday bonus; it means that a 15-year old user that created an account then left could have 240 points.
We can take away all the points at will anyway.
I don't really see the problem with it. I've always thought it was a little strange getting birthday points, though. I'd have probably based them on the account creation anniversary instead, but that's just me.
Just found out that you can change your birthday, so that means some people might just change their birthday to the next day to get more points.
For example, if their birthday is 2/4/2002 and it's the 2/4, then they can change their birthday to 2/5/2002 so then they get even more points.