It can take several months before all the hormones are flushed from the system. If he can currently be social with geldings and even other stallions, I would not worry much about him being aggressive/charging horses in the next paddock post-gelding. I wouldn’t house him directly next to a mare, at least for a few months, but with the situation you describe, I would be surprised if it was a problem.
Any chance he can be gelded & then return to his current home for several weeks?
