Age gaps (human F/Os)

I know some of you guys are fine with dating F/Os who are 300 years older than you, but they still look relatively young. However I'd like to ask... what about age gaps between someone and their human F/O? What is okay? What is not okay? How big should the gap between someone and their F/O be? Is it okay for someone in their twenties to date an F/O in their forties/fifties? And is it okay for someone in their forties/fifties to date an F/O in their twenties? Just out of curiosity