Okujima Hiromasa, Takahashi Hidebu, Est Em, Okadaya Tetuzoh, Asada Nemui, Totempole, Kajimoto Reika, Mentaiko (geicomi dj mangaka influenced by famous shounen/seinen stories), Iwasawa Midori, KOIKE Sadaji, ARAI Niboshiko, etc (the space here is limited, so no more creator names)
Also: https://www.reddit.com/r/Animesuggest/comments/17vufpd/are_there_any_shounen_manga_with_bl/?rdt=44199&onetap_auto=true
A very good list from RoseMary: https://www.mangago.me/home/mangalist/226060/?filt
Contains all old man and middle-aged man BL I could ever find. All of these guys are 35+(I know 35 year olds are not old men, but according to BL standards, they are). Mostly contains BL with old ukes or both of the guys are old men. There are some with old man semes as well, but it depends on whether I read them or find them.
⁃ uke always horny > nonstop sex drive – literally *begs* be fucked!
⁃ sexy ukes
⁃ tight hole defiled
⁃ peachy/juicy butt
⁃ huge dick
⁃ buff/muscular ukes
⁃ submissive ukes (w/wo BDSM)
⁃ rapist/asshole semes
⁃ taller ukes
⁃ younger ukes
⁃ student a/o teacher ukes
⁃ childhood/school/college friends
⁃ dominant/strong ukes
⁃ cross-dresser ukes
⁃ demon ukes
⁃ sukes/sekes (versatiles)
⁃ fuck buddies
⁃ friends to lovers
⁃ coworkers to lovers