I would like to add a comment about having a 12 year old (or ANYONE) shooting an air rifle..................it's the best thing in the world you can do to help him be a better Marksman. I'm dead serious!
My youngest son (now 16) was out hunting hogs & such with me by age 12. He can & could shoot any firearm I shot (shotgun, rifle, pistol, Black powder, etc) and do a good job too. But I got him into the Range's youth air rifle program about 3 years ago and the results are fantastic. He has improved so much that he just finished shooting at the 4-H Nationals a couple of weeks ago and may well be on his way to a schoolarship in shooting.
And what's even better........... I'VE learned a ton to improve my own shooting in the process with him. In fact, I REALLY have to work hard now to make sure he can't out-shoot me!
The bottom line here is that if you can be accurate with a low-powered airgun (match guns shoot around 500fps) you can shoot anything well. It is SO easy to throw a low-speed pellet off-course that it makes me feel absolutely SLOPPY firing my M1A - and yet still hit 8's, 9's, & X's when I'm doing it.
Practicing with a good air rifle is like swinging an "on-deck" bat before stepping up to the plate............................. it WORKS.