I was in your spot 8 years ago. Long time surfer, skater, wakeboarder whose body started crapping out. This book changed my life: https://www.amazon.com/Starting-Strength-Basic-Barbell-Train....

Strength training with barbells fixed all those aches and pains in my knees and joints that braces and doctors and physical therapy couldn't. When I started squatting, I suddenly stopped being afraid to walk down stairs. My posture improved. I noticed I had way more endurance when riding, and it made ever part of that, from carving to pumping, easier and better and more powerful.

For me personally, resistance training with weights is better than almost any other exercise for managing ADHD. I don't know what it is, but something about lifting keeps me focused and calm for a few days after a workout. Cardio never really did that for me.