Koi ga Ochitara
http://www.mangago.zone/read-manga/yuki_to_matsu/
http://www.mangago.zone/read-manga/koi_ga_ochitara/
http://www.mangago.zone/read-manga/oni_to_tengoku/
http://www.mangago.zone/read-manga/metro_dog/
http://www.mangago.zone/read-manga/on_doorstep/
http://www.mangago.zone/read-manga/doushiyoumo_nai_keredo/
http://www.mangago.zone/read-manga/boku_no_omawarisan/
http://www.mangago.zone/read-manga/gohoubi_ha_shitsuke_no_ato/
http://www.mangago.zone/read-manga/konomi_ja_naka_to/
http://www.mangago.zone/read-manga/mujaki_na_wanko_to_nekokaburi/
http://www.mangago.zone/read-manga/ren_ai_nenrei/
Some good bl manga age gaps stories where both of them are legal, guys. Thankyou!