fucking another man is not gay if he has the skin of a woman, meaning smooth hairless skin. whether he identifies as a woman or not is irrelevant.

fucking a 12 year old boy is thus never gay, but it is in most cases morally wrong, and in almost all cases a very bad idea ( unless you're both on a deserted island with no other humans ).

for a man over the age of 18 to have such a smooth and hairless skin he would have to in most cases be taking female hormones. though there might be some naturally effeminate men who don't grow body hair until later in life.

also it isn't really about who is top and who is bottom but who brings money / power to the table and who brings youth and beauty. this is regardless of who is penetrating whom ( in most cases it will be both ) and regardless of whether the bottom is male or female.