Studies have shown that domestic rats that become alphas develop more hormones and become more agressive. I'm betting that the same is true for wilds. I'm hoping along with you that proper parenting will prevent neutering.
I just adopted a 7 month old neglected girl, she won't leave my side or range out of sight of me, but I'm betting that she's really afraid of being left alone again.
On the other hand every normal healthy rat I've ever raised slowly started freeranging further and further as they got older and more confident. If your house can't allow for free ranging perhaps you might want to take a page out of my shoulder ratting guide and find an outdoor safe site for him to explore and romp about at. I can't see any real difference in the specifications required of the safe site except it should most likely be larger just in case. My part wild did great at the safe site, in fact she actually stayed closer to us than my shoulder rat did. And she was more reluctant to run out over open space then my domestic.
While I believe you could be able to avoid the neuter, I really have my doubts that a big healthy boy rattie (wild or domestic) isn't going to want to explore his universe sooner or later.
And by the way... when your little boy "ran away" he came back and found you on his own and he was much more capable than some people thought he would be. I know you are being a good dad and you worry about him, but don't underestimate him, if he's healthy and normal he's going to grow up to be a freaking amazing competent animal you can be very proud of. Your little bugger very well might grow up to kick your wild rats to the curb and out of his house.
And by the way, unless you have all metal cable wires in your walls, those wild rats are a real fire hazard.