Sorry it's hard to know exactly what you're asking. I'm assuming by 'prior authorisation', you mean from your health insurance company? This is something which varies from area to area, depending on your insurance carrier. Here's a little info:

Insurers have stated that the purpose of prior authorization checks is to provide cost savings to consumers by preventing unnecessary procedures as well as the prescribing of expensive brand name drugs when an appropriate generic is available. In addition, a prior authorization for a new prescription may help prevent potentially dangerous drug interactions.

It's not unheard of for this to happen with ADHD meds. Put yourself in your carriers place - they are expensive, potentially could be prescribed for the rest of your life and a type II controlled substance. I'm not saying I agree with it at all. It's useless bureaucracy second-guessing your doctor, but there's no reason why it won't be approved. ADHD does sometimes go away in adulthood, I don't believe that has been disproven yet. What has been disproven is that it always goes away. Here's one source at least:

More than 2 out of every 3 of those diagnosed with ADHD as children continue to have these problems as teenagers. 2 out of 3 of these will still have problems as adults.

This may be the reason they are doing this now, as some adults find they don't still require medication.