I agree with your first paragraph but not your second.
My sister is married to a younger man and there is none of what you describe. It depends on the couple. I think it was her illness that he was escaping from since he was the weaker of the two.
Yeah I know the personal anecdotes but the general tendency in older woman/younger man marriage is he will fool around. It took John Edwards a long time to do this. Or maybe he had other affairs with no babies that Elizabeth let slide
She wrecked her health by having babies at age 48 and 50 via fertility treatments. Perhaps .... just maybe this was her way of competing against younger gals John was seeing? Who knows and who cares because I like neither