I hate the fact that I stopped playing. Last time I played was 1994 when my college band received the Sudler Award and alumni were invited back to perform with the band.
I was a trumpet player and I have this same regret. I played thru my freshman year of college, nearly 25 years ago. But then my school dropped football, and as such no longer needed a marching band. So I moved on to other things.
I still get my horn out every once in a while and show off for the kids (they have no idea how really bad I am).