I'm of the opinion that it really is case by case and more important then the obvious age gap, the maturity level is more important. Women in general mature faster then most men. And it's possible a 45 year old man is more like a 25 year and the 20 year old female could be more like a 30 year old female. When I was 51 I had a 22 year old girl madly in love with me. As much as I was flattered and tempted to indulge in this because damn she was sooo hot, she was not very mature at all and acted more like 16 so I had to pass. So you see it's not as easy as a yes or no.