My boy was also in the wild until he was over 6 yrs old (he's 11 now) and after I had him about a year I put him in a small 5 acre pasture and quickly discovered he had no respect for fences. He saw some mares a couple of pastures over and he sailed fences like a deer. Luckily we had done so much round pen work in that first year that he knew it was time to come home when I approached. SO... he spent several months in a larger paddock with my husbands Belgian. They bonded as a herd pair and now when they go out to pasture with each other he no longer feels the strong call of the wild. It does get a little dicey when a large herd of deer or elk come through, but so far he just puts his head up, sniffs the wind for danger and does that awesome blowing sound that can be heard across the valley! A little anxious trotting but having the Belgian as a danger barometer has been very valuable. He's since learned that if the other horses are calm, everything is fine. (Although the smoke from our forest fires makes him understandably nervous)
In the end, there's no real way to know until you try! Good luck and let us know how it goes!