Hey Mikeskeins,
Dont worry it is your age, i had my first Flight Attendant interview with Qantas when i was 18 and made it thru to medical and was then told no, i the attended 7 other cabin crew interviews and made it thru to final stages and not hired.
like you i joind virgin blue as a Customer Service Agent for 1 year then on my 21st birthday i was finally recruited as a long haul Flight Atttendant with the Qantas Group, the recruiter who did my final interview remembered me from my Qantas interview when i was 18, ive have been flying for close to 2 yrs now and enjoy it.
Looking back I think 18 is to young to be a Flight Attendant i am happy how it worked out for me even at 22 now, i believe is an early age to start flying, as I am still young the life of a flight attendant is demanding on my life, so gain as much life experience and you will make a fantastic F/A one day.
good luck, it will happen soon enough
cheers
Australian boy