Any recommendations where the uke is younger like he’s a high school or college student ...

BL Motel has an adult uke/teenage seme coouple and a teenage uke/adult seme side story couple, maybe you like that. Also i recommend you
http://www.mangago.me/read-manga/yume_musubi_koi_musubi/

http://www.mangago.me/read-manga/i_m_no_match_for_him/

http://www.mangago.me/read-manga/koori_ga_tokeru_no_o_matteru/

http://www.mangago.me/read-manga/hitotsu_shikanai_mono/

Then there are also many teacher/student BLs with younger ukes, such as:

http://www.mangago.me/read-manga/suki_ni_nattara_dame_desu_ka/

http://www.mangago.me/read-manga/koi_ni_nare/