It depends on your comfort level, I think. If they're reliably perching where they should be, then they technically could go out to free-range at any point, as they should still return to perch in the proper location. I think I usually wait until about 3 months of age at the minimum, which is about where your littles are at, right? Be very aware of any hawk activity with OEGBs in the mix, though, as they're tiny and very easily snatched.
Wow, he must have been a lot older than you were told--seems like he was
huge compared to those OEGBs when you got them all!