I think the idea for his face is that due to all the hardship and experience he has (starting adventuring at a younger age) his face is more stressed so he looks 10 years older.
Wait, not only did they abruptly kick MC from the party, they even demanded him to relinquish his possessions?
AND HE WENT ALONG WITH IT?!
I completely forgot that MC was such a wuss.
Wait, that isn't an eggplant? Did the writer/artist ever see spinach? Wait, did I? No, I definitely did. Village born and raised. That is no a spinach of any kind. FAKE NEWS