I'm 56. I started in shotokan in my 20s. I switched to BJJ and did it for 20 years. I am now doing Shotokan again. I am way healthier doing shotokan. During BJJ, I always hurt. I train shotokan 6 days a week. Many times, morning and night. I have never felt better.
Age is just a number. I used to get sore in my 20's. I get sore now. No big deal. I think you just have to listen to your body, not take dumb risks, and rest when you need it. No different than when you were young.