Less than one in a hundred may be regarded as a tomboy, or in the case of a male, sissy without them being gay. But even if fully gay, it's not their fault they were born in the wrong body. You see it in homo sapiens, but hardly if ever in the animal kingdom.

I'm just gonna tackle this one from a personal straight shooting perspective. Yes. I HAVE pretty much always noticed that I'm attracted to tomboys and repulsed by sissies. I'm gonna also observe of myself that the one drag queen that I've know was sort of hot in drag and sort of repulsive in queer male mode. I've known several gay guys that are as or more masculine than I am, and prefer being around that sort than flamers (although, a few of them have been funny as hell, but often uncomfortably too sexually topical in their wisecracks for my sensibilities).

As for a personal relation developing in sexuality and personality expression, I think I would encourage males to learn to express positive masculine characteristics and females to express positive feminine characteristics, but I would also try to be supportive toward any efforts they were making to explore their own curiosities about social roles and expectations. Normal is an important aspect of a society. Walks on the wild side are allowed and encouraged, but grounding in normalcy is desirable.

What is "reasonable age"? 7? 13? 15 ?17? 20?

I have a question for you as well. Assuming your "cis" gendered cross dressing boy were in your locus of friends - and assuming you are a biological cis female attracted to boys...would you be attracted to this boy yourself? Would you like him to ask you to go to Prom? Suppose he is wearing the cutest little skirt or other feminine outfit on Prom night...and his makeup is flawless. Would you as a girl who is attracted to boys feel happy and proud to be escorted by this boy? Or would you in reality - in your heart of hearts be embarrassed. Would you be envious of the other girls whose Prom dates were handsome well groomed young males?
As a woman of marriageable age would you be proud to have a husband who openly wears womens clothing and wears makeup on his face? Or would you be looking about for a more masculine man to makes your heart flutter and your toes curl when he makes love to you...

Evolution for sexually reproducing animals is all about sex and nothing else. Fitness is technically defined as the number of offspring reaching sexual maturity and nothing else. In social animals it gets a little complicated because many members may not actively engaged in sex. It is further complicated by kin, group and multilevel selection. For the moment however we can simply acknowledge that as a sexually reproducing species it is not surprising that humans are very interested in all aspects of sexuality.

To understand why there is so much confusion over sex we first have to set aside the myth that humans among all animals are not primarily driven by instinct. What should be obvious is hidden by culturally induced cognitive dissonance. We can call it speciescentrism. The vast majority of the brains activity does not ever become conscious. Evolution is conservative, it does waste energy on the non essential. What becomes conscious is only that which increases fitness. An animal does need to know why it is behaving it only needs to be predisposed to behave in ways that increase fitness. By historical convention those predispositions are called feelings. They are called feelings because instincts are generally but not exclusive consciously experienced after the fact as physiological changes. For example thirst is not an instinct it is the physiological expression of the instinct to acquire water when certain other physiological conditions are meet. Sex functions in a similar way. Exposure to certain stimuli and the presence of certain internal physiological states will cause other emotional states (called feelings) to rise to a semi conscious state. In other words the presumption that humans are not instinctual is driven by the misconception that if they were we would be conscious of instincts. Keep in mind that the pin head size brain of an insect is sufficient to find a mate and engage in complex copulation. Don't expect that anyone is going to find the physiological origins of sexual instincts anytime soon. We actually have very little idea how they work.

Getting back to the subject at hand the vast majority of humans will be predisposed to engage in activities that lead to reproduction. At the kin level the vast majority of humans will be predisposed to encourage fitness of relatives. At the group se!ection level the vast majority of civilizations will be predisposed to have cultural practices that increase fitness. All the hypothesises that have studied possible increases in kin fitness due to such things as the gay uncle advantage have come up empty. At the moment homosexuality appears to offer no fitness advantage and thus no advantage to the species. That may or may not be true but the point is it is unreasonable to assign a moral stigma to a sexual preference driven by instinct. That would include the predisposition to want your children to sexually reproduce. Everything else about the discussion is abstract.

I'm not saying the abstract is unimportant, it is the key to understanding the cultural ape. What I'm saying is that social justice is more about emotional manipulation to satisfy the desires of the social justice warrior than to improve the health and happiness of the human race.