I agree that I would welcome a birthday recognition from AG, but rather than an AP boost I would want something like an email notification. Lol, I actually got one of those from the speedsolving forums and it brightened up my already-bright day! Also maybe you could get an armatar automatically on your birthday with a cake or something.
Giving AP is a terrible idea. But maybe a little image of a birthday cake or party hat or something next to your rank would be reasonable. Of course this would mean your birthday would have to be locked in from when you register. I think you can just change it willy-nilly now.