I see you've got various doubts. One small suggestion: when you say things like "I'm too old to compete at this gig" ask yourself if there is specific actual convincing evidence for that, or if you're just grappling with some near-term depressive thoughts. (Also, try gathering evidence for the opposite argument: That you'll compete well with your professional colleagues.)
I hope that didn't sound condescending. I definitely don't have any psychological training, just my .02. Having watched this industry for a while, I can assure you many of the people you think you're competing with will come and go with the business cycle and with real-world work challenges. People who really want to do it stick around through various bubbles and tend to do very well for themselves.