I'm young too (23) and I have extra skin on my stomach that won't seem to respond to anything. I just got to goal though, so who knows what will happen in six months to a year
Honestly I'd much rather be here with stretch marks and extra skin than at my starting weight. I feel so much better and I can't describe how awesome that is!
Strength training helped me minimize the extra skin though, I think. Unlike a lot of people I don't have flabby arms. Since I lift heavy my arms are pretty muscular actually! My legs are muscular too...just my darn middle doesn't seem to respond to any core exercises! Blah!