DTC question

My child was diagnosed with autism in 2025 at 6 years old. He was approved for the DTC from 2023 to 2030. So they went back 2 years. I saw they can go back 10 years. Is this something I should ask my doctor about or because he was diagnosed in 2025 at 6 years old is that the limit they could go back. I was just wondering because he was born autistic not something he suddenly got at 6 or even 4 years old. So is it possible to try to get approvel from the yera he was born?