Responses
You can just look up older uke in the tags . I don't know about grandpas but there are quite a few sexy old men ╮(￣▽￣)╭
I only know of this one http://www.mangago.me/read-manga/itsuka_no_yume_someday_s_dream/
any yaoi mangas with teen seme and somewhat old uke? I've been reading Jojo djs and I came across this one where Jojo loves his grandpa HAHAHAHHA (It's quite nice actually)