You've been a photog's asst. since you were 13? Do you work for free or for a parent?
When I was 13 people just couldn't get over the idea of a young kid doing things so I got a lot of business in pretty much anything I wanted to do. I was a freelance DJ and web designer and this local photographer (who was my basketball coach at the time) was really interested in my work and hired me to be his part time assistant as well as his full time video editor.
Weddings are an extremely easy business (to get into) but it's also an extremely competitive and stressful business if you aren't experienced.
If you want to shoot a wedding with an XTi that's fine, as long as you have some kicking lenses and some serious lighting equipment to go along with it. A lot of people with the same camera as you will be there, it's an extremely popular camera among wedding goers so you should have a lot of self confidence and remain assertive.