@Khrysaor Late 20s & 30s are only considered "too old" in Japan for women—the reason is misogyny. Japan is, unfortunately, a really misogynistic country still. It's very much ridiculous.
@Mielly Elderly people work for a variety of reasons: some simply enjoy working, but prefer a job that isn't as stressful as office work. (Janitorial work isn't fun for most, but it's also not stressful.) Often that's the only kind of work they can find, because age discrimination is very real. (They won't hire them for other jobs because they assume they'll retire and/or die soon.) Some need to work because they don't have enough savings/retirement income to live off of. Some do it so they have extra income to spend on themselves or (often) relatives, especially grand-kids and great-grand-kids. And some do it because they're bored. My grandfather did that, getting a job as an usher at the funeral home even though he didn't need the income. (He also was able to pre-pay for his eventual funeral at a hefty discount while being an employee there, saving him money and making sure his family didn't have to worry about paying for the funeral when he eventually died. Funerals are expensive, my mom died this summer (not from COVID-19) and it cost nearly $10k USD even though we did everything possible to keep costs down.)
Also your assertion that no one cleans floors for fun is incorrect. My grandmother enjoyed housework, to the point where she'd start cleaning my apartment when visiting if given the chance. One notable time she and mom arrived really early and had to wait for me to take a shower. She started washing dishes while I was in the shower. It may be uncommon, but it happens.
And they
shouldn't be laboring? They absolutely shouldn't need to for survival, but if they
want to for whatever reason then they damn well should have the right to do so. Along with the above, other reasons for going back to work exist. It's not uncommon for people to feel useless/worthless after retiring, and getting a job to feel useful again can be vital for their mental health. I'd much rather a 75yo work as a janitor than end up committing suicide because they feel worthless to society. (This really happens.) A similar thing happens when a spouse dies, as they feel lost without them. I'd much rather they get a job to fill their days than sit at home depressed over the loss of their spouse. This can lead to early death, not necessarily from suicide but just because they lose their will to live. It's
very common for the surviving spouse to die within a few months of their spouse's death.