Hey Yahoo answers people: When he asks about the gun being dangerous, my guess is he means "Is this a safe gun to own?"
There Beretta is a very safe design, but safety is more about the user. The best way to keep is safe is to not load a round into the firing chamber. The next best way is to load a round, then press the saftety lever down. This will dec0ck the hammer. After the hammer is down, you can leave the safety lever down or move it up. It is safer to leave it down, but you must remember to move it up before you try to shoot.
Brand new, probably $600 to $700. I've seen good used ones for $500 around here.
The age/ammo restrictions are not based on caliber, they are based on what gun the ammo is for. Rifle & shotgun ammo at 18, handgun ammo at 21. However, there are some rifles that shoot handgun ammo. Therefore, you cannot legally buy 9mm handgun ammo from a shop but you can buy 9mm rifle ammo from a shop.
As a note: if you're only concerned about home defense, look at shotguns. You can get a nice Mossberg 500 for under $400 brand new. A shotgun is much more powerful than a handgun and easier to shoot. The only disadvantage is the size. (It is a little hard to carry a shotgun in your pocket, glove compartment, etc.) Even so, most places restrict Concealed Carry permits to people over 21.