The subject was mature but it wasn't a hentai and I don't think it was 18+ but the premise is that in Japan the birth rate has dropped drastically so teenagers in school are encouraged to be more promiscuous. The MC is a guy who seems disinterested in it and the pressure put on him by teachers, parents, and classmates to actually have sex.

He and another male friend hangs out at an abandoned building blowing up condoms and talking, they even speak with some surprise that the condoms were actually supposed to be for birth control back in the day.

It ends with someone in power saying that their project is yielding good results and they want to lower the age of the promiscuity program.

Nevermind I found it

Shuuseki Kairo no Himawari story 1 Keep Those Condoms Away From Our Kids