Age is determined by trips around the Sun and sex is determined by genetics. Gender, by definition, is not determined by sex. You are conflating sex and gender, but they are not the same thing. You can feel like a man, but be biologically a woman. You can feel like 40 at 70, but you're still 70.

gen·der

/ˈjendər/Submit

noun

1.

the state of being male or female (typically used with reference to social and cultural differences rather than biological ones).

> People are male or female by genetics

Some (most) people. As with most things, the whole truth is not that simple.

Regardless, "sex" and "gender" are also not the same (though they're usually closely related). There's nothing about having a Y chromosome that makes one have short fingernails, short hair, unable to wear dresses or high heels or paint one's fingernails.

Genetics is not that simplistic. A male born with androgen insensitivity syndrome have every genetic marker for being male, with male chromosomes, but get female genital and female secondary sexual characteristics. AIS has a range from mild, partial and full, and is only one of many areas where you get gender variation.

There were a study that looked if biological sex difference in the brain matched the chromosome or the gender that a person say that they are, and it found that biological sex difference did not match the chromosome for transsexuals. It matched the gender that the person said they were. The study also concluded that hormone replacement was not a factor as they only tested those who had not gone through that.

This mean that genital and secondary sexual characteristics are not adequate to correctly identify the genetic sex, nor is biological sex difference such as brain composition, bones or other traits which normally differ between genders. DNA is the closest thing to a clean binary state, but then we have strange cases where some individuals have multiple DNA in them, and thus have both XX and XY. As such the best scientific conclusions is that both gender and sex is a probabilistic result of the combined traits that we associate with male, female, man and woman.

> Although, if you show me a random person, I can easily tell you their sex (and in most cases gender).

No, you think you can easily tell their sex, because people who have successfully transitioned are the ones you can't pick out. It's confirmation bias.

Maybe I don't understand your argument but it sounds like to me you would think that 3 feet long is societally determined because you need a social system to define what 3 feet is and create measuring tapes and whatever but that would make every metric socially constructed. It only works based off a different definition of what socially constructed means thqn I intended in my post so I could try to nail down a better definition or if you want you could suggest to me clearer words in the future but I'm loathe to get into a semantic argument here.

Edit: TL;DR by my understanding your definition of societally determined is so broad as to not really be very meaningful.

In what sense is the time since birth subjective?

Excepting general relativity time dilation Interstellar situations, that is.

Many people refer to sex as what someone is biologically and gender as what society considers them (edit: just FYI I'm not an expert and this is probably an oversimplification). While sex is more constant there isn't any reason gender has to be (and there are practical reasons why it shouldn't be but that's out of scope of this comment). This means that while biologically someone might have two XX chromosomes and be 60 years old it's not necessary that society considers them an old woman.

That's simply wrong. Age has a definition. You cannot 'feel' yourself into a different age. Sex != gender.

If they do (don’t have mine handy to check) then perhaps they shouldn’t. Since that marker is used to enforce a specific gender on people’s lives.