Preemie hitting milestones

When did your preemie “catch up” to others their age? I had a late term preemie due to health problems and didn’t think he’d be that behind but he still can’t hold his head up and I’m starting to get discouraged. He caught up in weight within the first month but physically he’s still way behind. This is so different because my first was two weeks overdue and hit milestones early.