I started noticing changes mid 60's but in my late teens I could do 100 press ups and etc with ease even though I'm not a lightweight. The ability to do 100 probably dropped off a lot earlier. I did a number of things from time to time to keep reasonably fit until early 40's but things wear out so did less
lot less, for instance I used do 5min or so every day on a pneumatic rowing machine hitting it as hard as I could.
DIY - depends. Strength can be a problem when things feel heavy now that didn't not all that long ago but the other problem is drive and back trouble can be a hindrance. I can't get the mental attitude back to do long winded jobs continuously. Eg new fitted kitchen, wall removed, floor levelled, some electrics, rerooting services, suspended ceiling and etc. There has been problems which has slowed things down, worst people who call themselves plasterers and time spent trying not to get one in. I paid a builder to add a new wall and a gas person to reroute the gas and disconnect a 2nd meter we had. 2 spinsters used to own the place and wanted separate bills.
So 2years later and it's still not finished but very little to do now - getting myself to do it is another matter. Having to keep the kitchen usable doesn't help. Sometime shortly I will finish off piping in a replaced and moved radiator. As that means some time on knees hunched up I might make the final parts of the runs 1 at a time.
Depends on how my back behaves. Some wall cupboards need moving a bit to centralise on the stove but wife has stuffed them full of things. Then comes tiling ............... Also fit the extractor - she's put stuff in the cupboard it's going in and just about all of them are jam packed full. She has loads more storage space than she had.
One satisfactory aspect is some one at Ikea told me that it isn't that unusual for people to take a year plus to do a kitchen. Given some of the problems such as levelling the floor in sections my 2 years ain't too bad but it should have been completely finished at least 6 months ago.