Our little guy isn't quiet eight months yet and has just started being able to push himself to sitting.

8.5 months holds sitting position and puts himself into the sitting position.

My daughter can sit unassisted but cannot get herself in the sitting position yet, although she is definitely trying. She was 8 months old last weekend

My son is 8 months and holds the sitting position very well but doesn't push himself to that position.

My little girl turned 8 months and just started sitting up on her own, so I'd say considering your lo was four weeks early they'll sitting up pretty soon! :)