We have only done mfm, 3 different guys.
One guy once, different guy 3 times, the guy we started with and still see pretty regularly, many many times with him.
We are mid 50s, wife is very attractive, not overweight, classy and polite. She likes men our age, clean, well dressed, classy and polite.
The one time guy and the three time guy fit that description. We thought a guy like this would be fun.
The one time guy was going great in the hotel bar, we were all getting along great. We all knew what we wanted and wife was REALLY into the flirting and conversation in the bar. We went up to his room, it was going well. They were kissing, got naked, she sucked him for quite a while. He started to fuck her and she was WAY into it until he started talking about how he was going to "fuck her like she'd never been fucked befor", how he was going to "destroy her ass hole". I didn't like it but I just let them play. Within two minutes she said that's enough, she got dressed and we left. Huge buzz ....... I was proud of her. It was too bad because the guy started out so cool, might have been great fun.
Three time guy, our age, very good looking, nice guy. I liked him. We saw him at his place and wife liked that. First time was very awkward, I just watched. Second time was more relaxed, he did her twice. She had fun. Third visit, he did her then I did her but he wasn't into going again after me.
We like our steady guy. He's definitely not her type but we have a great time with him. He 32, skinny need type, cool guy, just right aggressive. She LOVES sex with him. He(or I) have no problem doing her after other guy finishes and she gets off big time on that aspect and that makes it hot for all of us.
I'm sure his younger age has something to do with it but it's only a small part of the whole big picture and we have good fun with this.