Sophie was premature and is 5.5 months actual age but only 3 months corrected (what she should have been had she come on her due date!) We started weaning her almost 2 weeks ago, and so far we have given her baby rice, the Heinz banana cereal and Heinz yoghurt and fruit. They are both for 4+ months.
We have also given her butternut squash but we make everything really runny - the butternut squash we water down with her milk, and the cereals we make slightly runnier than the measurements on the packet - we're just trying to get her used to new flavours and textures and giving her the tiniest little bit! You are meant to wean premmies according to their actual age which is why we're doing it when she is still so small.
We have been using this chart and finding it really helpful:
https://www.hipp.co.uk/media/pdf/Weaning Chart.pdf