My wife's lover for the last three years is 16 years older then my 41 year old wife....
To be honest, I hesitated a lot when my wife told me that she wanted to try the man out, but I hesitantly let her do it and it felt alright watching him fuck my wife from behind in a shower late at night the first time, so I agreed to it.
Today I never think of the age difference. He's does his job very well with my wife, heck I've seen him fuck my wife for almost an hour straight and giving my wife countless orgasms before he finally gave in... He is kind to her and knows her boundaries and always asks if he want's to try something new with her. So I'm totally fine with her visiting him alone a couple of nights in a month or let him loan my wife for a weekend... The age gap is not even an issue today...