That was the Greeks. For the Romans, the aspect of mentor/student in a sexual relationship was seen as a very Greek practice - the Romans saw the relationship as more of a ‘master/servant’ sort of view. It was never acceptable for a Roman citizen, regardless of age or social status (‘infames’ excluded since they were already as low as one could go and still be a citizen) to bottom (though it happened regardless, of course, because social sexual standards are generally difficult to enforce).