How does one deal with not feeling like their chronological age?

Context: I’m autistic and have PTSD (actually diagnosed)

Sometimes it hurts so bad to see someone my age or even younger be more mature and put together than I am 😞 I feel like an eternal child… or maybe teenager? I hate it. I’ve always hit milestones later. From talking (started at 5), to walking (2), to even growing teeth (2 as well). Idk why I can’t just progress like a normal human being.