Its not about how old you are, its about nutjobs going by them selves, renting a gun and buying a box of rounds and emptying the magazines into others and/or them selves. Chances of you killing yourself (suicide) are much lower if you're with a friend/family member.
At my local indoor range they rent all sorts of handguns. Only up to .44 Mag though. You have to be 21 years old and its $10 to shoot whatever you want. Its a flat fee so it doesn't matter how many different firearms you want to shoot. You have to buy the ammo though which ranges from $11-$15 for 50rnds. Again, this is only at my local indoor range. Call around and see what the prices are. You'll need to pay for a lane, pay for the rentals, pay for ammo and pay for targets. I usually end up spending around $50 when I go there. That's including a couple hundred rounds. If I go to the outdoor range I only spend $14 + my own ammo.