But this whole argument is littered with ad hominem logical fallacies. And bringing cognitive biases into this is probably the biggest one of all, and the one that does least to strengthen your stance. All that does is try and discredit people by trying to prove that the reason why they believe something is wrong, rather than trying to prove that what it is they believe is wrong.
Great answer.
And I would think it would vary, as most of life does, with some starting pre 2 and others later - remember as Piaget taught, its the sequence of the learning that makes the difference, so that might push it up in some, back in others.
And, at this point, its pretty hard to come up with concrete proofs either way, and its not like it would be easy, but more like impossible, to come up with funding, much less human subjects, to test theories about sex and sexuality with kids under five. Its going to remain pretty much a mystery.