Autism and the army

Hi all! 
first post and I need some advice.  Sorry if it’s in the wrong place.

my son is 15 and has an ASD diagnosis.  He’s determined to join the army in the infantry and adamant he doesn’t have ASD.

to be honest I think the army is the best thing for him. My question is can I have his ASD overturned? He’s much more communicative now and makes eye contact (I understand this can be learned behaviour) Can I go private? Or would it have to be NHS (which made the diagnosis)

Can anyone give advice please? I’m going to make an appointment with his gp tomorrow.

has anyone been successful in getting an ASD diagnosis overturned?