I'm a 62 year old straight man. I've described the change this way.

I've always been able to see a handsome man, say Pierce Brosnan back in the day, and say "he is quite handsome" without have a whit of sexual stirrings. When I was young seeing a beautiful woman would trigger desires, but now it is like looking at handsome men. I can recognize they are attractive but it is purely intellectual with no emotional or hormonal attachment.