I've had conflicting advice. The BF counsellor said to wait until the adjusted age is 6 months, but to look out for signs of readiness (as per BLW). But I've also heard people with earlier (i.e. more premature) babies being told to wean as per standard advice at non-adjusted 6 months.
Twins were 6 weeks prem and we were told to do it at 6 months as normal. But tbh they weren't ready so I went with mostly blw and didn't drop milk feeds for a good while. They weren't my first so perhaps I was slightly less uptight about it so basically just went with them. I had terrible trouble with my first and I was determined not to go through the same thing again!! Let them take the lead and don't be put off by well meaning older people telling you they should be on 3 meals a day by the second day of trying!! On the other hand they could take to it like a duck to water.