Yaoi manga with longlast relationship? From high school to elderly.

All of Lust is pretty good - if you count that as lengthy...

I cant thunk of anything longer than that right now, unfortunately.

My apologies - wrong comment

Not quite elderly, but long time period.
http://www.mangago.me/read-manga/complex_manda_ringo/
http://www.mangago.me/read-manga/j_no_subete/
http://www.mangago.me/read-manga/new_york_new_york/
http://www.mangago.me/read-manga/life_senjou_no_bokura/

Life senjou no bokura ╮(￣▽￣)╭

Kimi to Parade and it's sequel Parade View have a quite long relationship too but I think they started from college. Sorry, my memory was a bit blurry.

*Paradise View