I agree with much of what's been said. Chinchillas can learn to tolerate a lot of things, doesn't mean they'll enjoy those things. Chinchillas are very social creatures and very individual in their personalities. I've seen chinchillas that just HAD to be on you, HAD to be handled, HAD to be a part of what you were doing. Others, not agressive, but could care less who you are other than the fact you were feeding them. It goes back to the nature v. nurture debate. I truly believe it's a larger portion nature for this particular issue as I've seen it all too often. Chins from certain LINES, regardless of their handling...don't want bothered. Chins from other lines, regardless of their handling...much more social with their people. Can it help to get them used to you? Of course it can. Will it help if you force them? Doubtful. Take thing slow, let them get used to you in the normal way (not necessarily HOLDING them) and see how it goes...nice and slow.
As for wheels, I would not personally offer a chinchilla under 10mos one. Most people say 6mos I think. Why? Why 6mos? Most chinchillas are NOT full grown at that point. Sure, they're a majority grown, but I like my animals to reach their full potential. Furthermore, it isn't going to hurt anything to hold off a bit longer but it COULD stunt growth if offered to soon. Error on the side of caution.