So how is he at recognizing numbers larger than just 10?
I have a 5 year old.
He can, say and recognize numbers even with 3 digits. And does not have to count it out.
You are not his parent. Does his parent, notice this too? Or thinks that it is a concern in any way?
How is the child, managing in school? Do his Teachers say anything about it? I would think, that in a school, a Teacher would notice and bring it to the attention of the parent(s).
As a layperson, you can't just "diagnose" him yourself. I mean, you wouldn't know what to look for, you don't have a DSM manual on you, you don't know how to then help him and what is appropriate to help him or not or that it will just get him more confused etc.
FORMAL help, has to be, gotten. From a Professional. Or the Teacher/school, should be directing the parent(s) to get an assessment.
Did you ASK him... ."WHY" he has to, count out all the numbers first, to then SAY what the number is????
Try asking him and see what he says.