Hi My Friend,
You will likely want to choose a shotgun that you can handle first. I would suggest a 16 or 20 guage if you can handle the recoil. If not try a 410 guage.
When you are using a shotgun for deer, I recommend shooting only slugs. Also whatever gun that you use, you should know it's limitations, by that I mean learn how far away that you can shoot at a target and still hit where you are aiming. If you would like my free ebook on whitetail hunting please go to the classified section on this site and you will see my post for a free ebook.
You will find a lot of useful information in my book as well as a few stories that I'm sure you will enjoy. You see most of us hunters started out when we were your age, and many of us had the same questions that you now have.
If you would like anymore info just let me know.
Learn all you can