the OP was talking about just knitting.. doing crosswords. A social life, and physical and mental activities are essential to keep you healthy and young. Look at the horrendous effect of the lockdown on so many people.... boredom and isolation are not good.
You're one of those people who simply cannot comprehend that not everyone enjoys the same things as you, aren't you?
Not everyone withers on the vine the moment they give up work, FFS. Maybe you would need to fill your life with organised activities and goals to be happy and youthful, but plenty of us don't. Plenty of people are just really good at occupying themselves off their own steam.
Not everyone feels 'boredom and isolation' when they're not working and/or surrounded by people. Lockdown had a horrendous effect on some people, certainly, but plenty of people emerged from it perfectly happy and unscathed. However, lockdown isn't a remotely comparable situation to retirement anyway, because if the OP was retired she wouldn't be confined to her house and banned from seeing people, so retirement wouldn't prevent her from doing any of things you claim would 'keep you healthy and young'.
but he travelled, did hobbies... My point was about pottering around, doing knitting and gardening
Gardening is a (very) physical activity. Knitting is a hobby. A crossword is a mental activity.
In any case, I'm pretty sure that the OP just gave knitting and crosswords as an example. I think you'd have to be pretty literal-minded to think these were the only things she would ever do with her time if she gave up work.