Haha hey anon - you know, I believe I’ve only ever had Bucky be younger than Steve once, and that’s in After Hours. Beyond that, I always have him older than Steve; usually it’s only by a year, though in some others (the stripper AU and the tattoo shop AU) it’s by 3-5 years.
Having said that, I don’t off the top of my head have a story where Bucky’s older and a mentor to Steve, although in Relinquished (which currently only has one chapter, I know lol), Bucky is twenty-six whereas Steve is only about twenty. In that one, Bucky doesn’t take on a “mentor” role so much, but the part he’s going to play in Steve’s life will be helping him relearn a bunch of stuff all over again, the right way this time.
Also, I have had a plot in my head for months now that I intend to write a little down the road that involves rentboy!skinny!Steve and businessman!Bucky. There are actually two versions of that trope that I want to work with - one lighter and funnier, the other darker and a lot more serious - so there’d probably be two different rentboy!Steve fics eventually, but in both of those, I imagined Steve only being about 19 or 20, whereas Bucky would be in his mid to late twenties. So there’s that too, I suppose. :)
I know I don’t plan to write anymore teacher!Stucky fic aside from A.H., because with so many possible AUs, I don’t see the point in writing basically another take on the exact same trope just so I can switch the roles. BUT if you had any suggestions for an “older!mentor!Bucky” and “younger!Steve” AU, feel free to drop it in my Inbox. :) I’m always open to listening to possible prompt suggestions, even if I can’t promise to write it.