As I thought early mediaeval.
For Hula's sake, I quote from the Encyclopedia Britannica, but that probably isn't credible enough a source for her, even though it comes from an eminent Oxford historian - as she will see he was a champion for the poor and needy, values important for early Mediaeval nobility and knights, extending into the Crusades:
George held the rank of tribune in the Roman army and was beheaded by Diocletian for protesting against the Emperor's persecution of Christians. George rapidly became venerated throughout Christendom as an example of bravery in defence of the poor and the defenceless and of the Christian faith.
George was probably first made well known in England by Arculpus and Adamnan in the early eighth century. The Acts of St George, which recounted his visits to Caerleon and Glastonbury while on service in England, were translated into Anglo-Saxon. Among churches dedicated to St George was one at Doncaster in 1061. George was adopted as the patron saint of soldiers after he was said to have appeared to the Crusader army at the Battle of Antioch in 1098. Many similar stories were transmitted to the West by Crusaders who had heard them from Byzantine troops, and were circulated further by the troubadours. When Richard 1 was campaigning in Palestine in 1191-92 he put the army under the protection of St George.
Because of his widespread following, particularly in the Near East, and the many miracles attributed to him, George became universally recognized as a saint sometime after 900. Originally, veneration as a saint was authorized by local bishops but, after a number of scandals, the Popes began in the twelfth century to take control of the procedure and to systematize it. A lesser holiday in honour of St George, to be kept on 23 April, was declared by the Synod of Oxford in 1222; and St George had become acknowledged as Patron Saint of England by the end of the fourteenth century. In 1415, the year of Agincourt, Archbishop Chichele raised St George's Day to a great feast and ordered it to be observed like Christmas Day. In 1778 the holiday reverted to a simple day of devotion for English Catholics.