Do you recall if he was diagnosed as level 1, 2 or 3? Mine was diagnosed as level 2 at the age of two. The specialist said he would put him at a 1 1/2 if he could but there is no such thing. Also the kids don't get as much early intervention at level 1 which really shouldn't be the case.
My understanding is level 1 is least severe, level 2 is moderate and level 3 severe. Besides language which truly can lag even in a neurotypical child, how significant are his meltdowns, sensitivities to sound, light etc...? Are you able to play with him on his level? Those are the kind of things maybe to look at and pay attention to. Just a thought.
Just to share, my son sometimes I feel is making great strides and though he is behind his peers, I think he will be ok. Then....something goes off kilter and he is non-stop stimming and can't be redirected. It is heart breaking to experience. BUT...truly looking at the beauty of their uniqueness I think is the goal, no matter the level of severity. Even in those that are severe..it is true that the behaviours come from that darn difficulty to communicate. Finding their triggers or being the psychics all us moms and dads are in training to be with these guys can help us slowly learn to understand what they are saying...then give THEM the words, or pictures to be able to express themselves. It's not easy or perfect. It's a journey and a rewarding one at that.
I will stop rambling now. Lots of hugs....

Is he receiving speech therapy? Is he copying any sound he hears? That would be your first clue. Encourage him to any sound he makes. My son said about less than 10 single words before starting ppcd at a public school. We didn't know he was on the spectrum, and we thought or wanted to believe that he was just a late talker. So we just kept reading him books everyday. It wasn't until when he was 4.5 that we noticed he started to imitate words and actions. Then his speech exploded after he turned 5. So when I took him to get his diagnosis earlier this month Dr. said the severity is lower because he is now talking. So you see, the severity does NOT stay the same. Keep giving him speech and read to him. He will surprise you one day.

My son just turned 6 & is finally starting to make progress with speaking little by little. There is no proven age where it is hopeless! Professionals still don’t know enough about Autism to give any solid proof and can’t predict a child’s future. HOPE is the key you need to keep within yourself no matter the severity. My son is living proof there is HOPE!

Unfortunately thats the million dollar qn, you are at this stage on your journey as many of us were. As time passed and our son went 2 then 3 non verbal then 4 and burned through early intervention (unsuccessfully) we finally did get MRI results showing areas of brain damage. By this time we knew he was severe needs, global developmental delay etc, diagnoses by us was before 2yrs as severe (we just knew) and it was comfirmed by just over 3yrs of age by professionals that he was severe so it was no surprise to us.
Acceptance comes in slow. Hope NEVER fades...the sooner you learn to go at your childs pace and not some cookie cutter "expected" milestonic pace and relax the better. Its not easy and sometimes involves a mourning of skills, tasks, events etc (our children simply set a pace they are not anxious with...)
Its a coming to terms and a roller coaster journey and condition..thats why we sre all here to support oneanother xx
You will love your child regardless, set aside your frustrations and "typical" development expectations x

Prayer, speech therapy, patience, great teachers, books and music is what is working for us. Prayer and patience are key.