Nice work. That horse looks pretty relaxed.
I've been working on a three young ones for the last year and a half. I was going to start them when they were two, but ended up doing lots of groundwork, for the most part. I ended up starting them as three-year-olds. They seem much calmer than they were a year ago. I'm sure that's partly from being handled, but I don't think waiting until they're three hurts at all, in the long run (and isn't that what it's all about).
So, yeah, I see nothing wrong with taking it slow.