Nika

Are you looking for a specific manga? If so, you would have to add more details :">

JUST READ HOW SWEET IS SUGAR DADDY
I just finished it and was awesome

http://www.mangago.me/read-manga/kokoro_kanda_neko/
http://www.mangago.me/read-manga/hidamari_to_bentou_danshi_to/

agreed with How sweet is a sugar daddy & Unfather, also the Kokoro series by Kanda Neko for something a bit sweeter http://www.mangago.me/read-manga/kokoro_kanda_neko/ , something vampire-esque so obvious age difference http://www.mangago.me/read-manga/royal_servant/?av=1 , Finder series (a classic, has some OVA anime adaptations) http://www.mangago.me/read-manga/you_re_my_loveprize_in_viewfinder/ , some nice smut and fluff and that arrogance of a young guy & spoiling seme http://www.mangago.me/read-manga/punch_up/ (it also has a sequel) , ongoing but if it's your cup of tea seme really is a silver fox http://www.mangago.me/read-manga/liebling/ , full colour big age-gap consensual whatever http://www.mangago.me/read-manga/a_paramour/ . You can search for "mangago older seme list" on Google and find a lot.

Age gap
http://www.mangago.me/read-manga/kirei_ni_shiteyo/
http://www.mangago.me/read-manga/jounetsu_kakumei/
http://www.mangago.me/read-manga/hatsukoi_no_tonari/
http://www.mangago.me/read-manga/yamada_to_shounen/
http://www.mangago.me/read-manga/oita_ga_sugiru_wa_koneko_chan/
http://www.mangago.me/read-manga/almost_paradise/
http://www.mangago.me/home/mangalist/209650/?filter=do
http://www.mangago.me/read-manga/suki_ni_nattara_dame_desu_ka/
http://www.mangago.me/read-manga/how_sweet_is_a_sugar_daddy/?av=1
http://www.mangago.me/read-manga/koi_ga_ochitara/
http://www.mangago.me/read-manga/on_or_off/
http://www.mangago.me/read-manga/lover_boy_lezhin/?av=3

For more Age gap you can follow my list
http://www.mangago.me/home/mangalist/607063/