interesting question. usually by timeline analysis, I just assume Whizzer is around thirty-four/thirty-two, and Marvin is something like thirty-six.
I don't know if it's canon but if Marvin and Trina married in their twenties, which seems the most likely for her/and his parents to force them, and then were married for ten years, it makes the most sense in my mind that he and she'd be like mid-thirties and then Whizzer kind of falls into that age range too.
also I think Christian Borle was fourty-two when he played Marvin in the revival, and Andrew Rannells was something like thirty-eight, if that helps at all (but I don't think they were chosen for age, and I've yet to look up Michael Rupert and Stephen Bogardus' age when they played the characters, so take this as you will).
does anyone on here know the canon ages for marvin and whizzer ?? ive tried to figure it out in my head but i wanna hear what yall think