There are only penis and vagina. Science has almost proven that transgender comes from a chemical miss hap in the womb. I support someone or anyone who decides this is who they are but from a science level is it real or just a mental issue?
Transgender is a real thing when being developed in your mother’s stomach everyone male or female start with a x chromosome that’s why men have nipples. women have xx as men have xy as there chromosome make up. through the process of development you may not gain a y chromosome until later in the pregnancy which would make the male feel as if he is a she. but there is NO such thing that makes someone genderfluid or make the identify as a animal, toaster, or both. so there is only two genders Male and Female you pick the one you feel and that’s the end of that.
If he means BIOLOGICAL SEX then you need to get it through your thick skull that does not mean what you feel on the inside in the real world no one cares how “you feel on the inside” Either you have a penis (male) or a vagina (female) you can be gay (I won’t judge but it does not change your actual gender no changing it unless you actually get a surgery
There is a lot of confusion about the meaning of the term gender. In academia (and LGBT vernacular) gender is something different than sex.
When a trans person shares their gender with you, this does not mean they are unaware of their birth (or current) sex. However, they prefer to be treated the same way you’d treat a cis person of that gender.
What this means depends on the individual, but you can start by respecting their pronouns, now that you know what they mean when they use them. I hope this clears things up a little bit.