Graydon Hoare began working on the language that would become Rust in 2006. Rob Pike began working on the language that would become Go in 1995. Neither of these are useful dates because the languages that were eventually produced were drastically different at their inception compared to where they eventually ended up.

For the purpose of maturity, the point in time by which to begin measuring the age of a language is the first point at which a stable release appears for general availability. Go is 9 years old, and Rust is 6.