My only concern is that this opens up a rather different can of invertebrates.
Elsa says no to (I forget his name) because he's a jerk. I would rather it didn't feel like, to the public, the reason was due to her sexuality and not his personality.
Steve Rogers is loyal to Peggy Carter, his lady friend from long ago, even though she has aged and he has not. He rebuffs Black Widow's advances because of this (I am basing my reading on The Winter Soldier
film). I would rather he still felt love, even with the age difference, and that is the reason to tell Natasha no. Not that she isn't lovely or desirable or the like; it's that he feels loyalty and obligation and love for someone else and is not free (in his mind) to pursue other interests.