I was about 14 when I began. By then I had freshly alienated myself from the Christian faith. (Now, I realize how similair my values are to certain Catholic or Orthodox traditions, just with different goals than them) However, I did not start to move past the whole "revolting against God" schtick until i was older. I learned magick worked at about 16 when I finally practiced it instead of just reading about it. It worked, and it worked well, surprisingly so. So I continued and have been to this day.
I must confess, to this day I look back on my past self and cringe at times. I am 23 now, and I find it so odd how I can grow so much in such a short amount of time. I am happy I did though, I was a mess back then. Not to say I am not now, everyone is, but more so then than now.