Re: A theory…
1- Where did you hear this gem? 
2- Unmarried or age? Two different qualifiers.
Did you mean to say general pissiness of married woman is NOT directly proportional to her age? AND A married woman is pissy regardless of marriage?
3- Third sentence talks only about not getting married. Age is not considered here.
I think first ‘pissiness’ needs to be defined.
I suspect you meant being an easily angered person or one who gets irritated easily.
Need these clarifications before answering. 