BB's and pellets are good.
Airsoft pellets might be good but wont give him a perspective that shooting things can be dangerest.
Paint balls... BAD iDEA ! Or A Nasty mess to clean up for someone !
I have used PPG paint on two cars quality stuff it was around $86 a pint for one and $$138 a qt for the other. House of Kolor has some cool stuff also , check it out !
CMMG and POF should not be used in the same sentence. Pinto vs a Cadillac comparison.
CMMG has had a lot of bad quality issues on the 300Black barrels as of late so I would steer clear for a while.