Its in some of our nature to mother men and/or women. I'm 27 years old and some women who are a little older mother me. I just look at it as them caring but it is odd
It's a nice thing to do. We love to provide or give comfort, well I do anyway, lol.
Some men let them because they've never been properly weaned (jumped from the nest so they could learn to fly) and for the women it fulfills a sense of being needed (mommies needing and enabling their little boys to stay babies).