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/
I'm looking for some yaoi about colleagues with an age gap
Something like:
http://www.mangago.me/read-manga/doushiyoumo_nai_keredo/
Or
http://www.mangago.me/read-manga/old_fashioned_cupcake/