In my personal case (I´m 74 years old now) my last dive was several years ago and I didn´t felt very comfortable as I do not practice sports and my job requires to be seated many hours at my desk with computer.
I´m completely out of training and when I had to don all the heavy equipment it was not easy for me to walk in the boat and specially when returning to the boat after diving with a bit rough sea the matters got more complicated for me. No problem underwater but the dive requires a lot of effort outside of water.
Probably I will dive again from a beach or pier and with a calm sea. Sometimes I´m tempted but I had not the chance. I miss the thrill of being U/W.
So, it is true that a diver can dive till an advanced age if in good health but also in good fitness condition.
I feel the lady you mention is Doctor Sylvia Earle. She must be near 90 years old now. I admire her so much and have been following her acomplishments since I was young.
I didn´t know she still dives! Curiously I´ve seen a picture of her while diving with a small sized full gold Rolex watch which was presented to her by the Crown Company.
Guess she deserves a gold Submariner!!
Best cordial regards, Abel