Everyone has given some great advice. While I cannot fathom doing that kind of mileage with no experience at my age- there is definitely something to being younger. Seems as we get older, we forget how to "just do it" and try something new (we overthink, overanalyze, have experiences that cause us to be more cautious, etc).
I've read lots of www.crazyguyonabike.com journals and young people do it ALL the time and succeed and have a great adventure. At night, after you've ridden for the day, read some journals on this site and read about people's cross country adventures. It's inspiring for sure!

I think you'll be fine. Your body will adjust. Just remember: TITS (Time In The Saddle). You need LOTS of it before the trip!!!! It might feel like a chore (or a second job), but you'll be better prepared for all that work you put in before.


Best of luck to you. I hope you have a GREAT time and I hope you'll keep a journal and keep us posted here on TE of your progress.
Oh- and let's see a picture of you and that bike!!