I worry about this too. I'm 26 and my surgeon said that exercise will help, but because I'm so young, I have plenty of collagen in my skin that I shouldn't worry too much about excess skin. The good thing, if it happens you can always have it removed.
If you're like me, I think "G-d, I hope it doesn't happen because I really don't want another surgery", but at least the medicine, science, and experts exist to correct the problem, should it occur.