I think usually it’s a late-20s/early 30s deal, and that’s if you’re basically going into academia for life.
Makes sense then…
But, yeah having a PhD at 22 means you are some ungodly genius or the messiah.
or alternatively the writers don’t really understand how academia works and just gave shu a dozen phds to emphasise that “this guy is smart”. it’s basically impossible to have multiple advanced degrees by 22 unless you literally did nothing but study, sleep and eat since your early teens. a more realistic depiction of shu shirakawa would probably look like