I don't think people are thinking in relative terms....Just the huge gap in age. Like I said, I wouldn't date one, but not because I think it's wrong....Both parties are full fledged adults. But I know I have NOTHING in common with a 21 year old chick.
If I were 45 and she 31....Hmmmm, I might give it a go....I figure she's lived enough to have had enough experiences that she had a firmer grasp on reality......But if it were 25 and an 11 year old, well I think you know where the jury stands on that.