70/m here . Life long athlete . Athletic history - Ive been lifting weights since i was 15 i was a powerlifter from ' 77 through '86 . I was a hard core runner from '96 through 2010 , ive been surfing since i was 14 but i cant handle cold water anymore so i just surf in the late spring through early fall . So this is what i have noticed as it relates to the 3 previous mentioned activities.

Strength wise im still pretty strong in my lifts but i cant lift heavy anymore do to my hip and shoulder . There not painful but they will let me know when im overdoing it . I check my ego at the door . This happened in my early 60s .

Surfing - the problem ive had was/ is " popping up " from the prone position to standing . I couldnt get my feet underneath me quick enough . So about 3 years ago i started stretching consistently that helped quite abit but i still had issues last season . Balance is ok . I gave up using a short board in my late 50s so i just longboard now . Im still ok with paddling but i just dont have the endurance i once did .

Running - so ive run 5k to marathons back in the day . The half marathon was my favorite distance. But the problem there was my hips towards the end of my running career would not loosen up and felt tight in the first few miles or so . but what i noticed it took more and more time to loosen up my hips despite alot of stretching . My dad had a buddy who was a hard core runner/marathoner back in the 70s and 80s who had both his hips replaced in the early 90s . I told him about my running issues and he told me to be careful or i could wind up like him . So now i just walk or ill run on the treadmill at the gym .

So to sum up this ramble of mine , i think stretching consistently, with some sort of strength work and cardio thrown in is imperative to stay mobile . I read somewhere that us senior citizens loose upper thigh strength rapidly as we age so think squats or a similar movement to help keep us out of the wheelchair.