You may be any age provided you are with a parent or legal guardian.
You must be 18 to purchase and own rifles and long arms.
You must be 21 to purchase and own handguns.
18 years old.
http://www.wikihow.com/Shoot-a-Shotgun
Depends on how old the shotgun is.
Depends on your parents
Get your brother in law to shoot it for you.
A shotgun can shoot up to 80 yards it it depends on what the choke is on the gun.
Yes if they have a liscense or a legally liscensed parent or gaurdian.
a 12 gauge shotgun can shoot about 30 yards accuracy
You should be OK with standard loads.
No
Depends on how old it is. Have it checked over by a good gunsmith
Pellets or slugs. shotguns usually shoot shot or pellets, but you can shoot slugs. in Indiana we use a shotgun to hunt deer and use shotgun slugs, better to use a barrel with no choke in it. cylinder bore preferred.