Hi

If you can give us a bit more info you will get better advice

Use of gun (think ahead), rifle, pistol, calibre, budget, springer, PCP, do you need a scope, bag, moderator charging cylinder etc.

Don't chase power, accuracy is far more important, and also consider the age and size of your lad, at 15 they can be 6 footers or still have a bit to grow, so not everything will be suitable

Sharing a gun is not recommended unless it's just for an occasional plinking session BTW