http://www.mangago.me/read-manga/mayonaka_no_oyatsu/
http://www.mangago.me/read-manga/nights/
http://www.mangago.me/read-manga/ai_no_kotoba_wo_uragaeshi/
http://www.mangago.me/read-manga/boku_no_shiru_anata_no_hanashi/
(not sure about the ones above since the ukes are around 30-40ish, idk if thats too old?)
http://www.mangago.me/read-manga/caf_latte_rhapsody/
http://www.mangago.me/read-manga/hanamuko_san/
http://www.mangago.me/read-manga/kaeru_no_prince_sama/
http://www.mangago.me/read-manga/kouun_no_rihatsushi/
Soko Ni Suwaru Na, Sore wa Isshun no Hikari dewanaku, Otoko Hiroimashita, Akutai wa Toiki to Mazariau, Suteneko no Karute, Restart, Mata Ashita, koi to wa yobenai, Soredemo Kamawanai, Osewa Shimasu, Sweet Chapel, Love Monster, Puchi Puri, Aisanai Otoko, Beauty Stock (2nd couple), Otona no Manaa, Dining Bar Akira
Stories where the uke is older than the seme (not too old) and its not a student-teacher relationship or a coworker relationship.