Baby not crawling yet and not good at sitting

I keep seeing all these posts with November babies crawling. My son is 28 weeks (about 6.5 months) and he isn’t crawling. He does crawling motions but that’s it. He cannot push himself up with his arms in plank position. He also can only sit up unassisted for about 30 seconds he hates it.

I’m confused because everyone we know comments what a strong baby he is because he legs and arms are SO strong when he kicks and grabs omg 🤦🏼‍♀️.

Is my son the only one who isn’t crawling or sitting up perfectly well?

He’s a big baby he’s in the 98th percentile height and weight and has a huge head, so idk if that’s affecting him...