My kits are up on the houses with mom within a couple days (5 inches high) and up on the shelves a little after that, maybe a week and a half old. I don't have high shelves though, mine are maybe 8-9 inches off the bottom of the cage, so it's not a huge distance. I wouldn't want them going 2 or 3 feet up at a young age, that would be quite a drop. I would be pretty careful of them getting up a lot until they are at least a month old, but I'm a bit paranoid what with all the broken leg threads I see lately. I'd rather keep them lower and safer for longer.