I don't agree with girls in their early 20s dating men in their 50s and above.
I believe that men in their 50s and above who go after women in their early 20s are sexual predators who take advantage of a girls naivety and also try to manipulate them into the woman they want them to be.
This might not always be the case though, age barely matters when the two get along very well.
It is all about the level of maturity that bring two persons together.
I believe that the right person for you is the right person, regardless of age.