My LG does this too - I think it's just her exploring her body and the ways she can move it!
You lo was born early so it’s normal to be “behind” as you say on milestones but honestly don’t think he is behind because every baby is different and will do milestones as there own time! These are guidelines! And also I think this is all normal my lo rocks back and forth sometimes in the high chair etc but my dad etc used to do this as a habit I wouldn’t even think about autism signs at this age.
I don’t think you can diagnose autism at this stage, however I would ask the GP for extra peace of mind! Babies do develop differently indeed, but best to ask and check if in doubt. That’s what I would do😊
it looks like he's just making grabby hands. probably means he wants to be picked up and not just left on the floor. my daughter does it all the time.
Please don’t worry; stimming is entirely normal for babies, it’s a way of regulating their psychological and nervous system, you may notice it is less prominent in the morning and increases as they become more/over stimulated. It can be an early indication of ASD, however there would be several (more reliable) symptoms present. These symptoms can be visible in infants, but mostly develop later in life. As previously said in the comments, work from “corrected age” for developmental milestones, and only use this as a guide. Try not to worry, I can imagine it’s weighing heavy on your mind. He’s absolutely gorgeous btw!
Tbf I think all babies stim to a certain extent because they're getting used to their bodies and they don't have loads of other ways to express their feelings! I know I've had similar concerns with my boy but I think it's just babies being babies xx