further to BG's excellent explanation of how to go through the claim...

Youth Allowance claims can take up to 21 days to be processed. You CAN apply online before the child turns 16 - I always recommend applying 3 weeks before the birthday so there is no delay between cancellation of FTB and the YAL starting. You can only be paid YAL from the date you lodge the claim if you don't claim on the 16th birthday.

In addition to a Tax File Number, you will need to supply proof of birth or arrival in Australia (e.g. original Australian FULL Birth Certificate,overseas passport with Australian Visa, or Citizenship Certificate) PLUS 100 points of identification (for example a medicare card 20pts, student ID card 20pts, bank statement 40pts and a school report 20pts).

A Youth Alllowance claim CAN be granted without a Tax File Number and with just 40 points of identification, but if the TFN and remaining POI aren't supplied with 28 days, the payment is suspended until the documents are supplied.

Schools will often apply for a TFN for students in year 9 or 10...if not, you can get an application form from Centrelink or possibly Australia Post outlets (not sure about this). A TFN application has different ID requirements to Centrelink. For 16 year olds, a birth certificate, a medicare card and a current student ID card will meet the ID requirements for the application - you can take the application form and the original ID documents to Centrelink and they will certify the documents and send the application directly to the ATO. Otherwise, the ATO need to see original documents and they have very few locations where you can lodge the applications face to face.

HTH!