the funny thing is, they way we imagine grown folks dressing is literally how they were dressing as kids back in the day too. they never changed their style and so over time it became associated with being grown as they continued wearing them as grownups. just a natural cycle
if every previous generation acted the same way we do, they would've tossed the suits in the trash as soon as they hit 30 and started dressing like their parents.
Every old head 50 and up would still be looking like this.
There really isn't any precedent for suddenly hating every fashion trend that was popular with your generation after you hit a certain age.
it's actually more weird to suddenly go from jeans and sneakers in your 20s to suddenly wearing peacoats and penny loafers in your 40s and 50s. that stuff didn't use to happen.