Interesting VN... A bit of a "breath of fresh air" imho.
Way it's written, leaves the mind going a bit.
On topic of as a few mentioned, so much grey hair before hit 30.
It's plausible.. Stress is a shitty thing, especially coupled with mental conditions.
My self, I had more grey hairs in my mid to high 20s, than now in my late 30s(barely none right now).
Being forced to find new jobs constantly cuz of cuts, lay-offs, what not.
And having to go back to the school bench for re-education. It's a bitch.
My gripe, is that the MC see himself as "middle-aged". While middle-aged is the period (age of 40 - 60),
before you're considered "old" (60+).
These days, cuz of the "second period millennials"(born '90-'96), it's accepted to call someone age of 37+ Middle-aged, in the US.
As it's the median of expected average lifespan.
(I'll always frown on that though!
But I'm neither born, or live in the US. So I'll go by whats globally accepted.)
Myself, I grew up being taught that middle-aged is the middle point of between when someone leaves the "nest"
(normally age of 20) to start their own life, and the day they would go off with pension(normally 65+). Which is 42/43.
(obviously some "leave their nest" sooner, or later, than others.)
Apart from that... Not bad! Not bad at all!