Theoretically we can report dates as young as a single year, but the margin for error may be greater than the date reported. On the other hand, if the sample is too old, not enough C-14 may remain for an accurate measurement. This means that the upper limit of C-14 dating is currently around 50,000 years ago.

Why is nitrogen-14 not an isotope?

They all have the same atomic number, same number of protons. Explain why carbon-14 and nitrogen-14 are not considered isotopes of each other? Because they are two different elements. Same mass number but different atomic number.