First of all you correct the age with the date the child originally would have been born. My daughter was 10 weeks early so when she was 2,5 months old she was new born. But it totally depends if there were complications and what type. My daughter didn’t have any severe complications and reached all her milestones at a normal age.

It all depends on the bubs, how premmie or any health issues when they were born. My son was 7 weeks premmie had issues and was a little behind but now hes 8 and smashing it

No, it’s not sensible to base a 3 month old premmie baby on the milestones of a 3 month old full term baby. You generally work out how old they would be if they went to full term, and base your milestones on that. But all babies are different, not even all full term babies reach milestones at the same time. Just love your bub, everything else will come along when it’s suppose to

I have friends with a premmie baby and they base his milestones on how old he would be if he was born full term. Eg he’s 8 months old but was 9 weeks early, so they set him at nearly 6 months. He’s nearly sitting up, which is his due date age milestone, not his premmie date. If that makes sense