User blog comment:SDPanthera/Fairy Tail Chapter 415 Review & Other Thoughts/@comment-1776824-20150111134714

Eh...I'm just going for Dragons can live for a very long time, but on 7/7/X777, whatever time they had left due to Acnologia leaving them half-dead ran out and they had no other choice but to hide inside their Slayer children's bodies. It is shown that Igneel was running, hugging, playing and touching Natsu, something we've seen that spirits cannot do. If they were corporeal then yeah, sure, but what I understood was that they were about to die on the 7th and in an effort to not do so they simply hid inside their kids, but before they could do that, they had to find children to raise, otherwise what would be the point. But w/e, the dragons are gone for good now and we can move on from the Tartarus arc.