I can understand asking for age verification on this forum and msot retailers. However, if some kids under 18 have AEGs that's none of your business as long as they didn't do it by lying. You can try to make it difficult but you can't take the law into your own hands and prevent kids from owning AEGs. What are the laws on ownership? I know in some parts of the US you have to be atleast 14 or 16 in other places but you can't stop me or some other teen from owning an airsoft gun.
I agree with fluffy (for obvious reasons) that you shouldn't push kids away where they'll do something dumb. Give them a place practice it safely.