I am 60+. I have certainly slowed down but consider myself to be quite active at this point. I still remember my mother at this age and think I am light-years beyond her activity level at a much younger age. And much of what I do is fairly 'extreme' for my age (at least I think so).
But as to yard work...I was out in one garden a couple of weeks ago... That particular bed is 30' x 15'..not small. I'm only about 1/2 way through weeding it to within an inch of it's life, along with some new plantings. It occurred to me at the time - don't plan your flower gardens/planting beds when you are in your 30's - they will come to haunt you in your 60's! I have another 10'x 24' bed; 2 more 3' x 15' and 2 more smaller beds yet to deal with. Sigh. And have 3 part time jobs that really stretch the available hours to manage those in addition to regular household chores.
But it all beats the alternative....