When Was the First Used Singularly?

The Oxford English Dictionary traces singular they back to 1375, where it appears in the medieval romance William and the Werewolf. Except for the old-style language of that poem, its use of singular they to refer to an unnamed person seems very modern. Here's the Middle English version: Hastely hiȝed eche . . .

When did we start using gender pronouns?

But she says it was from the 18th century onwards that people started using male pronouns when describing someone of a non-specific gender in writing and this marks the time when opinions on what pronouns should be used started to change.

When did they stop being singular?

You can find several authors who used “they” as a singular pronoun. When this grammar rule changed in the mid-1700s to declare “they” as no longer a singular pronoun writers still used it.