Sorry you have had no response to your question. I probably fall into that catagory you are talking about. I am ahh,,,rather old,,,and have some health issues as well. Though I am still able to teach, I have to be very careful not to hurt myself especially taking care not to break bones. It is very hard to dial things back after working and teaching "hard" for many years. Working out for those seniors who start their training late in life is different than someone, like me, who has been training for 35years or more and suddenly has to back off and work much more softly, if that is the proper word. It has taken a long time for me to accept the fact that I just can't pour it on anymore. I have finally been able to work my katas in a way that I feel keeps me mentally active along with the physical that helps me exercise. One should never overwork themselves to the point that they are hurting during the workout or the next day. Start working slow and easy and work up to a point where you complete each move and end with a certain amount of focus. The workout can be increased if your body tells you it's OK. Disicpline is very important, you become your own teacher.
If you have a broken leg, obviously you do not kick. If you are an older person, same thing. You work up to your own limits. Age itself should never stop one from working out. Just stay within your own limits. Hope this helps.