I am not really fixated on younger women, I like women my age and older too. But I do feel like it isn't socially acceptable for me to be showing interest in them if they are more than a few years younger. No not just 18, even if they are 19-22 many people would have a problem with it, including the girls themselves. This is a problem not only because I can't help being attracted to girls that young, but also because girls closer to my age and even a bit older often look insdistinguishable from those younger girls. For example, I find that it is usually very hard to tell a 20 year old apart from a 26 year old. So what ends up happening is that I am reluctant to show interest in girls my own age out of fear of them being "too young". Meanwhile the younger guys can approach these youthful looking older women without worrying that they might be singled out as a creep. I feel like all of society's regulations only serve to empower younger guys in their teens and early 20s and screw over guys my age and older. It often does seem to me like there is a deliberate attempt to make it the norm for men to date older women and taboo for men to date younger women.