We are pre-programmed for sex at an early age.
When I was about 7 years old, my aunt attended nursing school.
She brought her text books home and put them in an upstaies bookcase. Always curious, I had to check the books out.
There were pictures of all sorts of human anatomy. Males, females, pregnant women, fetuses in various stages of development, the different types of breasts, nipple detail, pendulous breasts, etc.
I probably knew more about female anatomy and pregnancy than any 7 year old around. The pictures of female genitalia were particlarly interesting to me and caused me to become aroused at even that early age. I would spend quite a bit of time studying the pictures and masturbating over the breasts and the details of the inner and outer labia and clitoris.
Obviously our brains are hard-wired and we are all pre-programmed for our sexual preferences long before puberty.