But I have a question. Why can't you exactly walk away from the opportunity and money? I have exactly walked away from it and was better off for it. Not everyone will be, no doubt, but the fact that I exist means that it is possible ;-)
About the only positive thing I can say about code I wrote in my 20s is it seemed like a good idea at the time.
Oh - and I work in a startup.
This is very comforting to hear! I'm 27 and feel the same way. I can only hope that I keep getting better at this whole thing, and that I can keep ahold of the feeling that I am getting better at it, as you appear to have.
You will feel the same way in ten years and in twenty. Except by then you'll recognize the pattern. I have seen lots of good programmers (I am not one) and the more experience then accumulated, the better they become.