Some of the most ADHD people I know are doctors; either emergency medicine or plastic surgery. You didn’t say if you want to get out of medicine entirely, but if you don’t these could be good options. I imagine that plastic surgery can be very creative.
Also, when you look at a whole life, your 20s are only a very small part of it. You have way more time ahead of you than behind you. 40 or 50 years is way too long to spend doing something that you hate and don’t feel that you’re good at. When you look back at the time in your life it took to learn something new, it will seem like a blip in time. You’ll laugh that you thought you were too old to start over. People change careers in their 30s, 40s, 50s, 60, and beyond!