I had the same problem with my mom, and one day i just brought home a Smith&Wesson spring pistol and promised her and my dad that i would be responsible with it and not shoot my brothers and always wear goggles. once you get it, the resistence to it by your mom will subside after a while. (i now own 6 airsoft guns including an L96 Sniper and Echo 1 M16, and my mom could care less. just don't be stupid with it.)
For those who are suggesting paintball, don't listen to them. Paintball guns and ammo are ridiculously expensive compared to airsoft, and airsoft guns outperform paintball guns in terms of fully automatic and semi automatic fire, and ammo is very cheap. The guns themselves are realistic looking, which is also a plus, if you are one of those people who like real guns.