While being no expert on the historical development of the english personal pronouns (I do read some old english and maintain some fluency in modern ditto, not my first language), the linked Wikipedia page clearly states the opposite: singular they came into use after the plural use.
This is a minor nitpick, as I suspect that third person personal pronouns where in a state of flux during the middle english period, replacing some inherited pronouns with pronouns borrowed from old norse. More so, language isn't defined by it's history but from how it is used presently!
I myself wouldn't use singular they, it goes against my “language intuition
” (probably formed by my native language which wouldn't allow that construction), others feel free!
This is a minor nitpick, as I suspect that third person personal pronouns where in a state of flux during the middle english period, replacing some inherited pronouns with pronouns borrowed from old norse. More so, language isn't defined by it's history but from how it is used presently!
I myself wouldn't use singular they, it goes against my “language intuition ” (probably formed by my native language which wouldn't allow that construction), others feel free!