I am 19 (close enough, right?).
Sleeping with the ostomy is no big deal. It's even better than trying to sleep with severe UC, because you're not getting up to run to the bathroom all the time. I did not have to empty the ostomy at night. The only thing that could be a problem is if you have skin problems/allergic reactions to the ostomy supplies. This happened to me at the beginning. I was allergic to a lot of the supplies, so my skin got very itchy and peely and the adhesives on the pouch couldn't stick to my skin very well. This meant that I was getting a lot of leaks, and I couldn't sleep soundly because I was always worried about getting a leak, and I was paranoid about rolling over and stuff because I thought I might cause a leak. But I got my allergies sorted out after a few weeks, I found products that worked for me, and it was all smooth sailing from there.
The smell is pretty bad, but the bag is airtight so you can't smell anything until you open it up to empty it, or if you have a leak. So you should only smell it when you're going to the bathroom; your friends won't smell anything. Plus, there are drops you can buy to put in the bag to reduce the smell when you're going to the bathroom too; they work very well.
The ostomy, in my experience, is so, so, SO much better than having UC. The only thing that really got to me was the body image; feeling insecure about it. This is probably more of a problem for young people like us. The thing to remember, though, is that it's temporary (if you're getting the j-pouch, that is). Plus, in time, my joy at being able to do the things I want to do and haven't been able to do due to UC far surpassed the insecurity I had about having the ostomy. It's a really good tradeoff, in my opinion.
Diagnosed with UC in 2007 at age 14. Three horrible flares, 11 blood transfusions. Tried, among others, prednisone (never worked), 6-MP (worked for a while), and Remicade (worked for a while) before running out of options and getting fed up. 3 step j-pouch; 1st 1/19/11, 2nd 4/20/11, minor complications, 3rd 8/24/11. Already LOVING my j-pouch!