I love Templar!England.
The Knights Templar was really all France's idea, and then he came over and bugged England about establishing a Templars' headquarters to raise men and money for the Crusades. And he seemed so cool and everything that England was like 'okay yeah'.
I'm thinking since England became a unified state in AD 927 (which is when I think of him 'coming into existence' or whatever), and France came over to get England on the Templar headquarters wagon about 1118, England would be in his mid-teens during that period. Like 16 or 17 maybe? I dunno, that's just my headcanon lol.