C. F. Keil and Franz Delitzsch on Ruth 2:21

Rth 2:21

Ruth proceeded to inform her of his kindness: כּי גּם, “also (know) that he said to me, Keep with my people, till the harvest is all ended.” The masculine הנּערים, for which we should rather expect the feminine נערות in accordance with Rth 2:8, Rth 2:22, Rth 2:23, is quite in place as the more comprehensive gender, as a designation of the reapers generally, both male and female; and the expression לי אשׁר in this connection in the sense of my is more exact than the possessive pronoun: the people who belong to my house, as distinguished from the people of other masters.