I had a desk job for decades of course, and was "tired" when I got home. After fixing dinner for the kids and cleaning up a bit, I would just sit watching TV or at the computer while the kids did homework or whatever. I would walk after lunch at work if weather was decent. And, I was drinking rather too much, mostly wine, which remains my weakness though I have curtailed it some.
I just signed up for an over 55 baseball league and have been to three "work outs", which I find tire me considerably, just standing around shagging balls is tiring. I keep thinking I'm not 30 any more, as if I need reminding. Ah, 30, I could "get in shape" for basketball in 2-3 days of running and be OK. I weighed maybe 185-190. Now I run a mile, shuffle really a mile, in 13 minutes if I push it. Then some folks my age can't run 100 yards. So, there's that.
If I could be disciplined enough to hit "it" hard and avoid snacking (I like nuts) and drinking and do something aerobic each day I'd be better, and that's my goal. I might try the fasting approach, I do it on occasion, mostly because I forget to eat if my wife isn't around that day. But, the fat you add at ~50 clings to you hard.
I think back about raising three young kids on my own and wonder how I could do it. You do what you have to do. And they were mostly good kids. They still seem to like me.