Oh yikes... Obviously the bitcoin stuff and buying Google stock early. Maybe buying a house earlier... But that's all money related.

Personally... Be less afraid to try stuff alone. I wanted to do a year of high school in the US for the experience, but nobody was able to join me so I decided not to do it. Later on, I told myself I would do those amazing travel destinations when I had a partner to do that with. Years later... I finally got over that and love travelling alone so much that I wish I would have done that earlier.

Careerwise... It's a hard one. On one hand I think I picked a fitting studies eventually (very beta). But doing something creative has always tempted me. I thought I wasn't good enough so I never embraced that. I would have loved to study architecture or something like that.

Oh.... and I would tell my parents not to let me quit my piano lessons.