I have the same question from a diferent perspective. The more matter you have around you/the deeper you are in a gravity well (same thing), the slower time runs. This question asks about time on planets; I want to ask about time in the center of megagalactic voids. Time runs faster there than it does inside a cosmic thread of galaxies. So when I see a claim that the universe is 13.8 billion years old, I wonder how old it is depending on where you are. Has anyone seen a contour map of what time it is in the universe?

Look up the Drake Equation. It will give you some more detailed starting points. Then also read this xkcd comic. It has something important to say about the discussion that unfortunatly does not affect the answer at all, but is still funny.