He was a young Tongue in training when left to join the Great War, and I would assume he was a brash 18-20ish year old at the time. So, add the years after the Great War to today, and there's his age. So, I'd say he is in his early 50s or 48 at the VERY youngest.
Don't think he fought in the Great War when he popped right out of his mom, or fought as a 10 year old (which was roughly when he was accepted by the Graybeards)