birth conflicts with their gender identity, which is a widely recognized medical condition that could lead to severe mental health issues if left untreated. Being transgender isn't a mental illness but the stress from not transitioning could lead to mental distress. Also, some transgender people never experience gender dysphoria.
Some children genuinely identify with a gender different from the one assigned at birth at a very early age. However, there are children who won't conform to gender norms, but won't necessarily grow up to identify as transgender.
Not every trans person wants or can afford sex reassignment surgery. Also, not everyone uses hormones or other medical methods in their transition. Everyone's transition is different in speed, methods, etc.
Gender identity is someone's internal, personal sense of being a man or woman. Sex is what genitalia you were born with (a penis or vagina). Transgender people are trying to match their physical characteristics, like their appearance or sex, to their gender identity.
Forty-one percent of transgender people surveyed in Injustice at Every Turn said they had attempted suicide, compared with 1.6 percent of the general population. Risk increased for those who reported bullying, sexual assault and job loss.