http://www.mangago.zone/read-manga/sayonara_alpha/
Only problem is the older one is the uke
15 yr age gap. My favorite. http://www.mangago.zone/read-manga/kokoro_kanda_neko
Older seme
http://www.mangago.zone/read-manga/yamada_to_shounen/
http://www.mangago.zone/read-manga/joou_to_shitateya/
http://www.mangago.zone/read-manga/oita_ga_sugiru_wa_koneko_chan/
http://www.mangago.zone/read-manga/otoko_yamome_mo_hana_ha_saku/
http://www.mangago.zone/read-manga/daidai_no_recipe/
http://www.mangago.zone/read-manga/yuugure_no_machi/
http://www.mangago.zone/read-manga/shoushin_otoko_ni_haru_no_arashi/
http://www.mangago.zone/read-manga/code/
http://www.mangago.zone/read-manga/on_or_off/
http://www.mangago.zone/read-manga/yuki_to_matsu/
For more Age gap you can follow my list
http://www.mangago.zone/home/mangalist/607063/
I would like to read mangas where there’s age gaps. I would like the top to be the older person and the younger to be the uke