I think 20 in third year makes sense if he graduated highschool at age 18, but that ID dates confused me (idk why I also remembered him being 23, my memories might've been juggled up with another character lol)
I tried to think about it and maybe that date is actually a return date, so by the time he's like 21 and he's in 4th year?? Idk if March is a normal graduating month in Japan tho — also I've never seen an ID like that so ╮(^▽^)╭

They say the mc's age is 20, but that ID clearly says his date of birth was September 28, 1999 and he got that ID at like March 2021, WOULDN'T HE BE LIKE 21-22 INSTEAD?? Am I losing it?