No one knows. It's part of the plot... Hehehe manga readers will understand and soon the anime only mashabiki will too. :) Remember the Battle of Fairy Tail arc. There was an enchantment placed kwa Freed so that anyone that were stone statues au were over the age of 80 years could not leave the guild building. Makarov, being over 80 couldn't leave but neither could the dragon slayers... Something for anime only mashabiki to think about. :) Some zaidi proof from the manga. Hiro did 'guild cards' for a few of the character at the beginning of Fairy Tail. If wewe want to check to see if I'm truthful then the site kissmanga has it, just look at chapter 23. Here is Natsu's: (It says 'Age: unknown')
Natsu is zaidi than 400 years old same as the other dragon slayers, gajeel, wendy, sting, and rougue all the dragonslayers who were trained kwa dragons, in the episode were Freed set an enchantment so only people 40 years au so under can leave the guild hall au something, that is why Natsu and Gajeel couldn't jiunge the fight of Fairy Tail, but they were able to after Levi lifted the enchantment
