Southwest plane had existing fatique on surface of plane

http://www.time.com/time/nation/article/0,8599,2062988,00.html

It says in the above article that the southwest plane that had a 5 foot long rip in its upper skin above the passengers, had existing fatigue from 39,000 cycles of compression and decompression from going to altitude (30,000 feet or above) and back to   Sea level to 5000 feet to 7000 foot airports here in the U.S.
They said the plane is 15 years old.