Saint Gregory of Sinai was born around 1265, and reposed on November 27/December 10, 1346.  He was thus an older contemporary of Saint Gregory Palamas, who was born in 1296 and reposed in 1359. 

Our patron, Saint Gregory of Sinai, has, as we say, three feasts and no services. He is celebrated on April 6 (and on some calendars, April 7), today, August 8/21, and on the day of his repose in 1346, November 27/December 10, the day we keep as our main feast.