try looking on here http://www.mangago.zone/tag/age%20gap%20/
Well I can only recommend you BL ^^; but here you go:
http://www.mangago.zone/read-manga/suki_ni_nacchau_yo/
(big age difference)
http://www.mangago.zone/read-manga/oh_my_hero/
(single father and young guy)
http://www.mangago.zone/read-manga/dear_ear/
(coworkers, one shot)
http://www.mangago.zone/read-manga/joou_to_shitateya/
(tailor and young customer)
http://www.mangago.zone/read-manga/winter_that_year/
(big age difference)
http://www.mangago.zone/read-manga/suterare_omega_wa_nido_naku/
(adopted father and son, omegaverse)
http://www.mangago.zone/read-manga/my_father_in_law_is_my_wife/
(father in law and son in law)
http://www.mangago.zone/read-manga/gohoubi_ha_shitsuke_no_ato/
(adopted father and son)
http://www.mangago.zone/read-manga/the_perfect_relationship/?auOf
(adopted father and son, really messed up so beware)
http://www.mangago.zone/read-manga/boku_no_omawarisan/
(former cop x new cop)
Can someone recommend me age gap story where the older person actually looks older ? I don‘t care if BL , GL, Shoujo , Seinen or Josei genre. I just wanna read an age gap story