There are two conflicting reports of Lord Darcy's age. In "The Muddle of the Woad" he's described as a few years older than the King, who's ten years older than the Duke of Normandy, who was 19 years old in "The Eyes Have It", which is set in 1963. This places Lord Darcy's date of birth around 1931. However, he's described in "The Spell of War" as an 18-year-old lieutenant in the autumn of the War of '39, which would make him about ten years older.