There are quite a lot of works with age gap,
a lot of shoujo has romance between JC/JK and teachers...
just from the top of my head (not all are really romance and I didn't read some so I don't know exact context)
P to JK
Mahoutsukai no yome
Full moon wo sagashite
kodomo no jikan
Koi kaze
Dengeki daisy
Musume no tomodachi
Chuugoku yome nikki
Oshikake twintail
My fair neighbour
gal gohan
hige wo soru ...
tbh if you weren't looking for a couplings where the male is older, I would have recommended Toshiue no hito
also I recall there being manga about JS/JC and public servant ... I think it was a gag 4-koma, but can't recall the name
oh, and although I don't know whether there is a translation, there was a light novel with name "Koushaku Reijou wa Kishi Danchou (62) no Osanazuma"...
Hm, that's more than i thought I'd recall...