It is common in colloquial English to use "they"/"their" as a generic third person singular. For example: "Could the person who left their umbrella please pick

It is common in colloquial English to use "they"/"their" as a generic third person singular. For example: "Could the person who left their umbrella please pick it up?" However, here it is used in a rather new setting for a specific and known individual. This is a rather new phenomenon pushed by the transgender and genderqueer community. I am specifically addressing the latter usage of the form 'they' in the third person singular. Do you agree this form is new? If not, could you give references to earlier usage than, say 1990?