ossan

Koi ga Ochitara: the uke is about 20+ years old and the seme is a about 40+ years old ( http://www.mangago.zone/read-manga/koi_ga_ochitara/)

Harapeko Usagi To Koisuru: the uke is like 18+ years old and the seme is about 30+ ( http://www.mangago.zone/read-manga/harapeko_usagi_to_koisuru_ookami/)

Kokoro: uke is pretty young and the seme is like 30+ ( http://www.mangago.zone/read-manga/kokoro_kanda_neko/)

Kirei ni Shiteyo: uke is in highschool and the seme is about 30+ years old ( http://www.mangago.zone/read-manga/kirei_ni_shiteyo/)

YAOI SMUT (everything else i recommended before was just regular yaoi):
Kono Ore ga, Ahe-goe Nante Dasu Wake ga Nai: ( http://www.mangago.zone/read-manga/kono_ore_ga_ahe_goe_nante_dasu_wake_ga_nai/)

I realized that maybe you weren't asking for age gaps or older semes but what's done is done. I've already typed all of these out

I HIGHLY reccommend Koi ga Ochitara. This is a REALLY sweet and cute manga

I was about to said the same
Yes, I highly recommend this story too..