Yesteryoung 

A man who is not old enough to be middle-aged but not young enough to fit in at college party.

why are you bringing your older brother, he's like 30 something. We don't need any yesteryoungs talking about their mortgage & student debt.

Yesteryoung by fspwest January 9, 2020

Yesteryonder

The day before yesterday

Jason: When did you get back from your trip?
Alex: Oh...yesteryonder

Yesteryonder by Hmmnmnmnm August 29, 2017