That is kind of a weird one. A lot of airlines will say "please apply again in 6 months." I have never heard of this before personally, but then again anything can be said/done in this industry. I assume that they are saying that they are going to keep your application/resume for six months and during that time they may call you again for another interview. They could also be saying like a said above that they want you to apply again in 6 months. There are many airlines that will give you an oppurtunity again to interview. From what your saying, it sounds like they do have interest in you, but there are people presently more qualified. I would not take this as them saying you are not good enough. Good Luck!!!