At 75 years old

I went to visit my 73 year old father in La a few weeks ago and he's never been on his roof in the 16 years he's lived there because there's no reason to. Beautiful 75 to 85 degree weather every day nice and sunny. But guess what? He's absolutely out of breath just going from his seat to the bathroom and back.
I know the stuff I do right now at 51 makes me tired and I feel I'm too old for it sometimes but I know it's what keeps me going.
Edit, now I have to get outside and get those wheel bearings out!