I've voted in every election since 1971. Now you know how old I am.

I registered at 18 in Kentucky when you still had to be 21 to vote in most other states. I still remember my grandmother telling me what it was like to be able to vote for the first time when she was in her mid-twenties. Its something I try never to take for granted.
My understanding is that you can register to vote at 17, provided that you will be 18 on or before the next election day. My son will miss the next presidential election by 2 months.