Does he also use Delayed Echolalia eg. pieces of dialogue phrases or words from TV or films? The
Speech and Language
Therapist should be able to tell you more about it. I would specifically be asking for a Speech and Language Therapist who also has experience of autism.
Does your son mix up his pronouns eg. I, me, you, yours, mine, us etc.
What is your son's social interaction skills like?
Are there things that your son is good at eg. puzzles, lego, pattern recognition etc.