You’re thinking about jobless reincarnation
Honestly, this gave me the same vibe. Otherwise, why would they us us panties of teenagers and the tags are harem and this man is cleary old. He either was early 20's, or late 18's. died. Lived for another 16 years and is now mentally 36, nearing 40s and picks up women left and right, it's like 'pick up dungeon girls' or smth. I don't know.
although the math aren't wrong there are more nuance.
a teenager living again in a child body wont have adult experience. I usually always think for isekai, their mental age are stopped until the body followed growing up. although this is just my headcanon and you're free to believe otherwise... but if you think like the way you think rn, unfortunately you will miss a lot of isekai story with romance or love interest.
what's funny is that this story doesn't even have proper romance. the mc hasn't shown any interest either sexually or romantically to anyone. he is basically aroace. the fan service and the girls are imho mostly for readers enjoyment. if you don't enjoy that, then this is simply not for you. there's no need to use strong language to piss off other readers
in conclusion it's funny that you even here
40 or 50 smth old fuck, gets married to teenagers