I'm not sure how to answer this question. Are you talking about my age as a corporeal body or the age of the atoms that "build" me. Then we have the problem that the quarks that make up these particles don't really have an age as such. Not to mention that we all have trace amounts of radioactive materials in our systems that constantly decay. And if I run by you then I'm in a different reference frame, so our ages are undetermined if we haven't kept track of that. And finally there really is no way to tell for sure because of the Heisenberg Uncertainty Principle.