Good Question.
I think it´s about circumstances.
Like, if i had a affair with a younger women, maybe 20 (my wife is 31), then a younger vs. older fight would be definitly great to watch.
But in my Fantasy it´s more like that the Fights, i would wish to see my Wife in, grown with the Time.
I mean, when she and a Friend of us had a Quarrel and where close to fight against each other, they where 19 or so, and these Fantasy is still going on. I mean, they both are 30+, but still i hope to see them fight it out.