You can sometimes tell a gay man, before puberty hits. A boy who is more comfortable playing dolls with girls, has little or no interest in playing with other boys - while still sexually immature - is not the typical ‘norm’.
Then ask yourself, as a young man would you willingly alienate your family, be rejected by your aunts/uncles/cousins/neighbors and your High School friends, and turn down intimacy with girls - in favor of finding some other guy? Would you willingly sacrifice employment opportunities, be an embarassment to your family, embrace a lifestyle that has extremely high incidents of violence, suicide, drug abuse simply because of an amoral bent?
In my limited experience, the Gay men I have met have pretty much always been ‘odd’. They were ‘different’ from the early elementry years. At that point, I doubt they had any real idea what they wanted, or why they wanted it.
To put that into perspective, at most in the U.S., there are fewer than 430 children born with this genetic disorder out of 4,300,000 live births per year. If the maximum number of Homosexuals are born a year, 3%, which is probably high, there would be 129,000 born yearly. Yet they have been unable to discover that illusive ‘Gay Gene’. Anecdotal, possibly, compelling certainly.