I am not much for the idol subgenre (though it's better than giant fighting robots, of which I had my fill early in my anime and manga explorations.) A notable exception is the anime Zombie Land SAGA, which is in a class by itself with respect to both its parent subgenres, zombies and idols.
Ossan Idol! is pretty much the same as any other idol-group tale, except with aged-up protagonists, if persons in their mid-30s can be called "older". Which... actually connects it to ZLS, in the sense of "let's think of the most unlikely possible people to become idols." (Which are Japanese pop music stars, for those just catching up, which seems to be a highly manufactured fame if these representations are anything to go by.)
Our central protagonist is a 30-something overweight shut-in who gets interested in dance via the internet, goes to gym, meets new friends, emerges from larval cocoon as a hottie. Practicing, he records his dance number at a karaoke room, accidentally uploads it to the net when he's trying to save (I relate), and it goes viral. Hijinks ensue. Third member, a failed dancer, is added to the nascent group because he knew the second dude, which injects a needed skills-mentor. They enter a local dance contest, get scouted, and that's about as far as Vol. 1 goes.
I said this wasn't about adolescents, but socially, these guys kind of are; unmarried, with dodgy unrewarding career states, at loose ends and flailing; Protag #1 even still lives at home with his parents and sisters. (One of whom, fortunately for his first public performances, is just trained as a hairdresser.)
I'll read the next three as they surface from my library.
Ta, L.