Adult is not an age. You and I both know someone who is over 60 years old, but not an adult. And there are 15 year-olds who show a lot of maturity.
Elderly is not an age. A friend of mine celebrated her 92nd birthday square dancing. She still drums for her band and drives Amish to wherever they want to go.
I still square dance and teach at the one room school. I have a few aches and pains, but manage. I'm 83. I gave up mowing this year (I love to mow my big lawn with my push mower) but I decided to save my energy to sew quilts.
And we all know of people who can barely walk at 60.