as someone who has dated a 20 year old (I was in my early 30's at the time) and met many others her age through social situations... most 20 year olds are just kids still, something I felt at the time and moreso these days... my tastes though really heavily lean towards maturity, it was a weird coincidence we even got into a relationship

And not all 20 y o are models. People with little romantic experience tend to fit better with younger women because women of the same age generally have more romantic experience