User blog comment:Hjetland/some ''ground rules''/@comment-32419585-20181124084421

Singular they is found in the writings of many respected authors. Here are some examples, arranged chronologically:
 * "Eche on in þer craft ys wijs." ("Each one in their craft is wise.") — Wycliffe's Bible, Ecclus. 38.35 (1382)[19]
 * "And whoso fyndeth hym out of swich blame, They wol come up…" Chaucer, "The Pardoner's Prologue" of The Canterbury Tales (circa 1400)[20]  quoted by Jespersen and thence in Merriam-Webster's Concise Dictionary of English Usage.[21]
 * "Eche of theym sholde ... make theymselfe redy." — Caxton, Sonnes of Aymon (c. 1489)[22]
 * "Then shalt thou bring forth that man, or that woman (which haue committed that wicked thing) vnto thy gates, euen that man, or that woman, and shalt stone them with stones till they die." - King James Bible  Deuteronomy 17:5 (1611)

Singular they is completely acceptable and hisorical.