pronoun, possessive their or theirs, objective them.
1 nominative plural of he, she, and it.
2 people in general:
They say he's rich.
3 (used with a singular indefinite pronoun or singular noun antecedent in place of the definite masculine he or the definite feminine she ):
Whoever is of voting age, whether they are interested in politics or not, should vote. A person may apply only if they are over 21. They have been an actor since childhood.
Words mean what people who use them intend them to mean.
But if you want something more authoritative than random-internet-comment, definition three from dictionary.com has you covered:
https://www.dictionary.com/browse/they
they
pronoun, possessive their or theirs, objective them.
1 nominative plural of he, she, and it.
2 people in general: They say he's rich.
3 (used with a singular indefinite pronoun or singular noun antecedent in place of the definite masculine he or the definite feminine she ): Whoever is of voting age, whether they are interested in politics or not, should vote. A person may apply only if they are over 21. They have been an actor since childhood.