A few years ago, a good friend and the husband of my permaculture teacher told me about the adult ‘growth spurt’ he had in his late twenties. I was around 23 or 24 at the time, and he told me he was a twig in middle and high school, then had about the same build as me, ~5’10, 160lbs when he was 22 or 24, and then late twenties really filled out to over 200lbs.
I registered that and occasionally thought of it, but mostly forgot it. Well, sure enough, I’m that age now, and filled out a good bit too. This was partly due to a conscious decision to put on size, but maybe it was spurred by some second puberty type drive.
Anyway, not sure if there are common and observable patterns here, or if it’s the same for men and women, but there are at least some anecdotal reports of it.