Now that I'm in my thirties, I can answer this. Two things come to mind.
First, really should have just done college after high school. I really wasn't looking forward to more school after graduation and wasted about 5 years before going back for my CS degree. I'm in a good place now, but could have had a 5 year head start on life if I'd just gone straight in.
Second, please take better care of your health while you have it. I was skinny as a rail in my early 20s and sort of took that for granted. I'm not obese or anything right now, but as you get older keeping in shape takes conscious upkeep. Get in the habit now and it'll be easier to maintain later. It's harder to lose the weight once you have it rather than keep it off.