At what age your autistic child starts talking or communicating with you ?

Hi everyone . 

my child is almost four now .. and he speaks with few words and two words sentence . However, he knows all the right words and speaks like singing and sometimes he ask for things politely like “green ball please “ . I also speak to him like he understands me when I gave him something I ask him to say thank you and I talk to him like he can answer me . 

I believe he is recording at this point lol , and I am hopeful one day he will speak and communicate. My question is , at what age did your autistic child start speaking? How has their speech developed since then? What strategies have you found to be effective in supporting their communication skills and overall progress?