Worrying about Milestones

My twins were 29 weekers, and we were monitored closely by early intervention and a NICU follow-up team for years. They were both behind on developmental milestones and we had therapy (PT, OT, speech) for many years... I spent a lot of time worrying about them being behind and not keeping up with peers the same age.
They are almost 4 1/2 now, and almost fully caught up. I find myself wishing I hadn't been so consumed with where they were developmentally - and just let them progress as they needed too. When we left the NICU we were told that it can take 5 years for micropreemies to catch up to their actual age - and that's been true for us. By the time they start kindergarten (in a year) they will be exactly where they should be.
I started early intervention as early as I could, and I think it really helped - I was proactive about it, rather than waiting for an issue to show up and then trying to solve it. The extra therapy really helped with their deelopment and allowed them to progress. We started to learn that although they were behind their same age peers, they were continually progressing at their own pace, and continuing to learn new things. The biggest thing I learned is that all kids (preemie or not) will achieve developmental milestones at their own time, and in their own way - there is no perfect timing. You sorta have to sit back and let them do what they need to do. Don't concentrate so much on what and when they are doing things, but rather are they learning new skills in their own time frame - do you see an improvement - and that's all that really matters.