Stork
My advise is gonna depend on where you live and your shooting conditions. Basically, get something you can shoot on your own, out in the back yard or in the basement, even if that's an air gun. Get a quality one, and the practice is invaluable.
If you're out in the country and can shoot in your back yard then get whatever the traffic will bear. You can't buy it, an adult will have to, and technically it's theirs, but we all know how this works. My SuperBlackhalk was "mine" but was and is my son's favorite, starting when he was nine shooting light loads.
Your mom shoots, so you have an ally in her. Get an adult to teach you safety, reasonable use, and proper ways to clean and care for the weapon.
If you're gonna shoot centerfire, learn to re-load. It cuts the costs considerably, teaches you safety, respect for what you are doing, and your mom will appreciate it if it lets her practice more, too. I began at age 16, loading for my dad's 30-30 and my 16 gauge. Again, find an adult who will teach you. If you don't know anyone, ask around at your local gun shop.
If you're stuck in the suburbs, don't despise a good quality spring air pistol or rifle. Black powder Silouette shooters use them to practice with, so you can too! It will teach you trigger control, aim, breath control, and a host of other things as well.
It is likely that you will soon end up with something with which to practice (air or .22 or .17) and something else with which to hunt. If you have supportive parents start with the practice piece and lobby hard for the hunting piece.
Anyway, that's my $.02.
Wayne the Shrink