My twins were 6 weeks premmie. DS was showing signs of readiness at about 5mths corrected age, and the other, DD, was a month and a bit later. We had a false start initially, where DS went OK for a week, then it became painfully slow....sounds similar to what your baby is doing. I gave him a break for about 1 week, then it was like a switch had been flicked, and he was away. My GP was very critical that they hadn't been on solids earlier, but they simply were not ready and there was nothing that I could do to change that.