Leonardo di ser Piero da Vinci, more commonly known as Leonardo da Vinci, was an Italianpolymath of the Renaissance whose areas of interest included invention, drawing, painting, sculpture, architecture, science, music, mathematics, engineering, literature, anatomy, geology, astronomy, botany, paleontology, and cartography.
The point in the timeline they visit him is 1464 when he was ~12 years old, yet he has a full beard despite being a preteen, just like Charles Dickens.
Leo, as a child, is depicted with pale skin and a long grey beard. Brad even calls him a "bearded kid". He has a white shirt and black pants, and he wears a purple and pink robe over it. He wears big lilac boots and a floppy purple hat.