22 rimfire yes
(Buckmarks, Ruger MKs, and S&W revolvers highly reccomended)
I don't get the responses re: rifle instead of handgun re: learning safety, muzzle control, etc.
no different for an 18 year old than a 36 year old or 54 year old, any 1st time handgun shooter
learning the rifle does not teach handgun control, no matter your age - for that you need a handgun, and no matter how expert a rifleman or wingshooter, it a whole other ballgame that can only be learned by way of instruction and practice
somebody oughta' tell Uncle Sam to quit teaching those 18 year olds to shoot handguns, restrict 'em to M4s and RPGs only ??
(if you truly believe you can teach handgun muzzle control with a rifle, well just teach 'em muzzle control with that BB rifle)
5 year old no, 18 year old yes, if want to learn handgun shooting, get 'em a 22 handgun, any flavor you/they prefer
and encourage them to vote RKBA