How does AARP know I'm turning 50?

Yesterday, I got my AARP card (!) in the mail (I turn 50 in December). I remember thinking when Drake got his card a few years ago, how to they know he's turning 50??

I was sure Drake and I were not the only people asking this question, so I typed into Google "how does AARP know I'm turning 50".  Here is what I uncovered (from the AARP web site):

We're pretty aggressive about recruiting new members. Right now, we're at 35.2 million and growing. The question people always ask me is, "How does AARP know when I turn 50?" I tell them we have this system of geo-synchronous satellites that circles the earth and keeps track of everyone… I even had one member come up to me in Dallas and say, "I'm not too worried about finding Osama Bin Laden. I figure that when he turns 50 AARP will find him."

Well, I guess that settles it then!