Actually, and this is kind of a weird one, this is often used as a racist joke but it is based on something resembling fact.

When I lived in the far east (I'm caucasian/white btw) I had a number of Japanese and Korean friends, who were aged from about 20 to 28 (I was the same age).

Naturally I'd heard this joke before, but I remember it came up when one of my female friends (probably the eldest) talked about her family wanting her to get married before what loosely translated to "the change". Now, being western, I thought she meant menopause, but I also thought that was weird because she was only 27 or so.

I got to ask her about it later and she clarified, saying she didn't mean menopause. She said that there's a stereotype even among Japanese people for there being "four ages" for women; basically "child, teen, adult, old" and that it was well-known that some Japanese women retain their youthful looks until quite old, but then seem to age quite fast in a short time.

I mentioned to her that obviously I'd heard of this idea, but I thought it was just some racist joke. She said that it was a bit of a joke even for the Japanese, but there were certain things which fuelled it - one example she mentioned was how in anime, characters tend to be kids, or a nebulous teen/adult age, adults, or old, but not so often in-between.

She said she was envious of western men and women in a way, because she believed westerners aged more gradually. She was honestly scared of waking up one morning and looking old, because apparently this happened to her mother.