I've been thinking about this now and again. IMO gender, if one insists on tracking it at all (which I mostly find counterproductive), would need to be a vector / tuple of floating-point values. The components would be something like:

1. Sexual Development Index: Encodes chromosomal sex, genitalia, and other primary sexual characteristics (X/Y chromosome ratio).
2. Hormonal Balance & Secondary Sexual Characteristics: Combines hormonal levels and the resulting secondary traits (body hair, muscle mass, etc.).
3. Brain Structure: A dimension indicating how a person's brain structure aligns with typical male or female patterns.
4. Gender Identity: A measure of self-identified gender, representing the psychological and social dimension.
5. Fertility/Intersex Traits: A combined measure of fertility potential and the presence of intersex traits (e.g., ambiguous genitalia, mixed gonadal structures, etc.).

Ideally it would track the specific genes that code for all of the above factors, but unfortunately science hasn't got those down yet.

Gender is not a boolean value, it's a variable.

We may have discovered gender entropy, Shannon would be proud

mmm... a long long

0100100100100111011011010010000001100001001000000111001001101111011000100110111101110100001000000110000101110100011101000111001001100001011000110111010001100101011001000010000001110100011011110010000001101101011000010110011101101110011001010111010001110011

No Y = 0

Presence of Y = 1

Looks like you can express it with binary if you want, though you would need an interpreter

As it is not stable I'd go with a database.

Sqlite.