Claiming PIP for 16 year old

Good Evening, 

My son will be turning 16 in a few weeks and therefore his DLA will expire. The DWP will continue to pay his DLA into my account until a decision has been made about the PIP (if we apply for it of course) It would be helpful for him to have it but I just wanted to ask any parents / carers out there about their experience in claiming for PIP for a 16 year old Autistic. The DWP have advised me to send as much information as possible to them when claiming, such as his EHCP, reports regarding his medication from CAMHS etc. But I understand that they sometimes ask for a face to face interview. 

I have also heard (in the media of course) about so many people being turned down for PIP. Has anyone made a successful claim for PIP for a 16 year old? If so how did it go for you and is there any further advice you could offer us at all please? I'd just like to arm myself with as much information as possible before we get the ball rolling.

With many thanks in advance, 

Rae