When I was 30 I used to imagine what it felt like being 50. Now I am 55 and it's not as bad as I used to think. I did modify my behavior a little bit and I don't take as many risks as I used to, I also try to avoid injuries because it takes longer to heal up and recover than when I was younger. I still like to have fun on my MTB but I am a lot more careful now. Strength training is really important after 50. I started strength training when I was 42 and still doing it today. 1-3 bike rides per week and 1 strength training session per week seems to work very well for me.