Sometimes mentorship is simply being the person you needed when you knew less.

You know precisely what would have helped at an earlier stage, because you were there and nobody provided it. That knowledge is unusually specific and unusually valuable, and there is always someone currently standing where you stood. Being that person for them does not require expertise so much as memory.

Think about what you needed at twenty, or at the start of a job, or after something went wrong. Offer that to one person. It rarely takes much time and it lands with unusual accuracy.