It reminds me of a friend I have who is quite severely depressed and has gone through a wide range of sexual identities. Straight, to asexual, then gay, then polyamorously bisexual, and now back to monogamously straight. Each change she excitedly explained to me that she had unlocked some deep secret to her identity and now her whole life made sense. This happened well into her adult years, not adolescence.
Some people seem to have a strong sense of a "missing piece" in their lives, and might be susceptible to latching on to almost any identity or community if it can explain that feeling.
EDIT: Because of the current barrage that trans people are under, I should clarify that I know trans people who have a deep and abiding certainty that their gender is different from what it says on their birth certificate; my above comment is not meant to include those people.