Fossil ages

Paddy is approached by a visitor at the Museum where he works as a Security Guard.

Visitor: "Excuse me, how old are these fossils?"

Paddy: "5 Million and three years and 6 months"

Visitor: "Wow, that's precise. Is that Carbon Dating?"

Paddy: "No,

Spoiler:

they were 5 Million years old when I started here and that was 3 and a half years ago."