Age gap between a man and a woman in a relationship

What do you guys make of the statement below; written by a commenter on this blog, Felix E.

A real marriage is unmistakably legitimate and natural and the age difference is usually convincing - within 8 years. If the age difference between a man and a woman goes way beyond this range, it's usually because the woman is extremely desperate to get married or that she's after material wealth.

Hmmmmm...do you agree?