I agree with thatkrayz - space is a major consideration both for movement and for safety. And as part and parcel of this, the disposition of your gelding has a direct effect on how the two will interact in a confined space - he could do a lot of damage to a younger weaker animal if he is inclined to so.
If you can set up a separate pen/corral (as suggested by Quinn) so the two can meet and greet over a shared fence (no barb wire, please) that will go along way to seeing how they will eventually interact with each other. If it looks like they're doing well, then the youngster can go into the bigger area. With regard to age, if your gelding is dominant and the new one is timid (or vice versa), there may never be a right age for them to share a smaller space.
Last edited by Chevaux; 12-19-2013 at 03:05 PM.