Provided you are not a convicted felon, you can buy long guns at 18 and hand guns at 21.
For a long gun you have to be 18. For a handgun you have to be 18.
You can buy the gun at www.japan-toys.com
buy one or find parts and build it
At most paintball fields and online. It is a new gun and will be easy to find.
You need a lawyer to find out for sure.
A great place to look for guns for sale is on www.gunbroker.com, there are also many store in areas that sell guns, If you find the gun on gunbroker, you will have to buy the gun through a FFL liceanse holder
You can find gun stocks online and in a gun store. Unless you know exactly what you need and what fits your gun, it is wise to ask the staff at a gun store about it.
You can buy books, send it back to the maker or find a gun smith.
Buy the latest gun digest to get up to date LIST prices
Contact your local police.
Federal law says you have to be 18 to buy a long gun and 21 to buy a handgun. Find a lawyer familiar with firearms law to get a correct answer to your registration question.
cap guns don't have bullets they just have blanks but you can find them at buck or two