The key to playing into your 40s is stay active and light on your feet. A lot of you that are older and even younger sound like you need some yoga in your life. I've been doing Insanity:Max30(30 minute workouts) for the last 6 months or so and I know it's a high impact work out, but that really helped with strengthening my knees and getting me light on my feet again. I'm back to running twice a week(3 miles one day and 7 miles on the weekends) which has helped with the stamina. Between doing Insanity, Running, Yoga, and basketball I'm feeling like I did in my mid 30s. I seen a thread in TLR where everyone was shytting on Offset for only curling 40 pounds, but in all honesty that's all you really need unless you're trying to be super strong. At that point that's different goals. I curl with 15 pound dumbbells and I'm stronger then most people. There was a time when I thought my knees were shot and I was done. I was sitting around making excuses on why I didn't want to workout, but I decided to go back to working out everyday and not making excuses. The more I worked out the faster I got and I was in less pain. I'm back to having abs again and low body fat. I'm not dominant by any means on the court, but I can hold my own for my age and surprise a lot of people with how much energy and stamina I have.
All the workouts I do are so I can play basketball, but playing basketball is the hardest workout I do. I'm always in pain after a good run. We usually run full court for about two hours.