If they are aged between 16-20 they need to be in full time study.The young person’s study must assist or allow them to complete a Year 12 certificate or equivalent qualification. FTB can actually go up to age 24 depending on the situation. That would be if they were a dependent full time student. The income test is higher for FTB then youth allowance. So alot of families that miss out on youth allowance due to parental income may still be eligible for FTB. You cannot claim both payments.
CCB can continue for as long as a child is in approved care. Primary school children are covered and I think that is until around 12 years of age however teenagers aged between 12-18 with a disability are also covered.