Legally, sure. But my non-professional opinion is that middle-aged men who want to date 20 year women are likely to be emotionally stunted and more interested in females as sex objects than as living, breathing, aging equals. Sometimes people will try to argue "oh, I don't want to only date 20 year olds...I have just happened to find my soul mate in someone less than half my age..." to which I say if you really want what is best for a 20 year old, let her find a nice 20 year old to date and experience young adulthood with. I hope this helps.