Sounds like the selection panel got it right on that one!
Holly, hard to know if its gone back to the years where over 30s had no chance. From what I know the Jetstar cadets were all very very young. I think it would be fair to say that things have slowed right down and now companies have the option to pick and choose. I guess the younger applicant gives an extra 10 year return on investment. I'd say there have been times (during the boom) in the industry when the opposite was the case.
In your shoes I'd keep applying for the cadetship and elsewhere if flying is what you want to do. You'll have a million hurdles, knock backs and down times during your career how you manage them will be what makes the difference in the end.
I actually remember picking up an info form of a large European airline in the early nineties. It stated: minimum 2000 hours and under the age of 24. Put the fear of god into me but I didn't let it stop me.