User blog comment:Stone Roger/Natsu and Zeref have somekind of relation?/@comment-90.210.218.195-20130225172826/@comment-7418318-20130329165751

I have a problem with that. In all the flashbacks (and the travel back in time in OVA 3) Natsu is noticeably younger and seems to be growing up at a normal pace.

So unless he was frozen in time I don't see how he can really be over 80. My best two guesses would be that the Dragons implanted something from their bodies into their pupils to enable them to use Dragon Slayer magic and this little bit triggered the runes, or that it was actually Natsu's scarf (and a similar memento from Metallicana somewhere on Gajeels body) that triggered the runes. Remember that Wendy was able to "heal" the scarf after it intercepted Zerefs magic. Could Wendy heal something that wasn't at least partially alive?