Try to teach him the lambda calculus. Church-Turing thesis still holds today, so if he's able to learn the lambda calculus he will understand what functions are

Try to teach him the lambda calculus. Church-Turing thesis still holds today, so if he's able to learn the lambda calculus he will understand what functions are indeed computable, and what functions are impossible to compute, regardless of hardware, software, etc. You don't need to have a computer (Von-Neumann et al didn't have one!) to invent a brilliant algorithm.