Joel (played by Pedro Pascal) is 56 years old in The Last of Us. In the first game he is 52 years old, and in The Last of Us Part 2, he is 57 years old.
The part 1 remake released in 2022, confirmed Joel’s age. You can check Joel’s date of birth by using Photo Mode while he is giving over his passport. We had never known his exact age before, instead estimating it based on context and other minor things.
Part 2 takes place around five years after the events of Part 1, and since Ellie is 19 in the second game, we may fairly infer Joel is 57.