The ONLY requirement for being trans is to say you're trans!

You need a diagnosis of gender dysphoria before you will get HRT.

There are criteria for that.

From the DSM V:

The DSM-5-TR defines gender dysphoria in children as a marked incongruence between one’s experienced/expressed gender and assigned gender, lasting at least 6 months, as manifested by at least six of the following (one of which must be the first criterion):

A strong desire to be of the other gender or an insistence that one is the other gender (or some alternative gender different from one’s assigned gender)
In boys (assigned gender), a strong preference for cross-dressing or simulating female attire; or in girls (assigned gender), a strong preference for wearing only typical masculine clothing and a strong resistance to the wearing of typical feminine clothing
A strong preference for cross-gender roles in make-believe play or fantasy play
A strong preference for the toys, games or activities stereotypically used or engaged in by the other gender
A strong preference for playmates of the other gender
In boys (assigned gender), a strong rejection of typically masculine toys, games, and activities and a strong avoidance of rough-and-tumble play; or in girls (assigned gender), a strong rejection of typically feminine toys, games, and activities
A strong dislike of one’s sexual anatomy
A strong desire for the physical sex characteristics that match one’s experienced gender
As with the diagnostic criteria for adolescents and adults, the condition must also be associated with clinically significant distress or impairment in social, occupational, or other important areas of functioning.

The DSM V also has transgender people without the dysphoria. But in that case, you don't treat with HRT or surgery. You just go: That's interesting. Have a good life.