The number of protons in isotopes of an element is the same.The mass number of an isotope tells you the number of protons plus the number of neutrons. Mass number = number of protons + number of neutrons â¢ Carbon has three isotopes: carbon-12, carbon-13, and carbon-14.
The 2nd time gap was long and came during Gaiden when Sarada and Boruto were 11 and by the time The Last : Boruto The Movie was aired, Boruto and Sarada were already 12 thus making Sasuke 33 years old at the final movie.
From this it can be concluded that Natsu is at least 14 years old. That is the only thing we can know for sure. But as to how old he really is, there is no definite answer. The Battle of Fairy Tail suggest that he might be older than 80 years old, but it was never mentioned explicitly that he is.