You remember being 18 months? That's spectacular! (My first memory is from when I was 26-27 months old, and nothing much self-conscious -- a boat trip on a river in then Yugoslavia.)

I have a fair sized description of how the process works and what I did to embrace nurture and deny nature. But nature won in the end.

To reiterate what I wrote, nature-nurture interaction can involve influences during babyhood, which lead to biological developments that stay with you for life (thus also limiting possibilities of further culturally-induced biological changes in later stages of development). On the other hand, you (still) like football and trains, two areas with rather strong gender imbalance, so maybe you did effect some later lasting changes in yourself, too.

A further point to make is that what is "manly" and "womanly" can on ocassion differ greatly between cultures. There is that African tribe (the Bororo?) in which it is young men who paint themselves, whose beauty concept involves perfect teeth, gracility and dance, and who perform in a beauty competition for the sturdy women to pick from among them. These men have a concept of manhood which compares to the concept of womanhood of a "cross-dresser" in Western culture, though in the first case it's nurture and in the second nature that seems dominant.

_{*Lunatic*, n.
One whose delusions are out of fashion.}