Concerns about Functioning Level

I had written to you last night, and I am so sorry to bombard you with more questions! My son who is 7yrs old was diagnosed with asd, originally when assessed they told me that although he is highly intelligent, he functioned 2-3 years below his chronological age. Is that typical, for children with asd? And will his functioning level ever catch up with his actual age? Sometimes I feel like that gap is only broadening, my concern is have a child who is 16 with the mental or emotional function of a 3-4yr old.