His earliest dated drawing is a Landscape of the Arno Valley, 1473, which shows the river, the mountains, Montelupo Castle and the farmlands beyond it in great detail.
The skull's eight teeth corresponds to someone of approximately the appropriate age and a silver shield found near the bones depicts a beardless , corresponding to the king's appearance during Leonardo's time in France.
Since Leonardo wrote with his left hand, it was probably easier for him to write from right to left.