Why can't Natsu and Gajeel go through Freed's runes? On Fighting Festival arc (Laxus arc) in chapter 108, Natsu and Gajeel can't get out from the guild because of Freed's runes.



But the rule says that statues or people above 80 are not allowed to get out from the guild. So why can't Natsu and Gajeel get out?
I would like to add on to Qynn's Answer:

In the most recent chapter of Fairy Tail, Chapter 400: 


  It was revealed that Igneel was residing inside Natsu, OR was using Natsu as a portal from the place where he was residing to come to Earthland. If Natsu had such magic imbued into him that could cause interference with the barrier as logically speaking, the barrier prevents those of age 80+ to leave and if it's a portal for someone of age 80+ to leave the barrier would automatically stop that person from leaving OR Igneel was actually inside Natsu not just using him as a medium and that would most definitely stop Natsu and Gajeel from leaving the barrier because they have someone of at least 300 Years of age in them. Since dragons are extinct, it would be safe to say Igneel and the other dragons are at least that age.