User blog comment:Sargenttacos115/Natsu and Gajeel age Theory/@comment-65.129.167.247-20141119010906/@comment-7418318-20141119012931

The reason why they couldn't go through the runes has already been resolved in the manga. Let's say they carried something with them that stopped them from getting through.

So far all the Dragon Slayers seem to age normally (save for the time spent frozen during the timeskip obviously). We got plenty of flashbacks of the younger Natsu and at least one of a younger Wendy. We've also seen flashbacks of younger Sting and Rogue. The only one who we didn't get a flashback to judge how quickly (or not) he grew up is Gajeel.