Age 24. Shot my grandfather's BB gun when I was a wee thing (6-7), some time off until the Boy Scouts taught me to shoot clays (12ga and 20ga, both missing frequently) and .22LRs.
Some time off until I turned 21, bought a Glock 19, joined the army, shot a whole bunch of Uncle Sam's goodies, bought a 10/22, came home, bought a whole lot of other guns, and have been shooting ever since.
Mostly informal stuff, but I've been to a few classes here and there (locally and at Front sight), and am looking into some action-shooting stuff here in Tucson. We'll see how that goes.