User blog comment:Sargenttacos115/Natsu and Gajeel age Theory/@comment-90.224.60.253-20140724120615

I actually have 2 different theories: 1st is that Natsu and all Dragon Slayers are actually the dragons itself with altered memory. As Dragon Slayers learn to attain features of dragons they are actually full bloodied Dragons. However they have forgotten this for the sake of the future. So they are slowly relearning to use their true powers. Igneel is actually Natsu, who has timetraveled through the Eclipse project. Natsu's existence is a loop result of the Eclipse project.

My 2nd theory is rather simple. Natsu and all Dragon Slayers obtained a part of their dragon's soul to be able to learn Lost Magic. This doesn't make them as old as their dragons but the "soul" inside of them still carries its age, preventing the Dragon Slayers' bodies to pass through the rune wall.

Enjoy :)