At one point I free ranged 6 chameleons in the same apartment, so it certainly can be done. It's not as daunting as it may sound!
- The youngest chameleon I started free ranging was a nice sized 3 month old panther, and he did great from the get-go. They don't really need to adapt to it slowly, you just move them over and they'll settle in within a couple days, like they would to a new cage.
- I don't think it's a matter of age, but a matter of size. Or not, depends how escape proof you make it. A fellow member, JannB, free ranged her baby veiled right out of the egg and since the free range was escape proof there were never any issues with her not finding the veiled.
- The big things to consider are: Escape proofing the free-range as much as possible, considering what to do with water, and cham-proofing the room a bit (just in case.)
- To escape-proof, I think the easiest thing to do is either (1) make the free range up on a table or something so the chameleon cannot climb down or (2) build a little fence around the perimeter of it. These animals can't climb smooth surfaces, so just 10" or so of something like plexi-glass around the free range, on the floor, should be enough to keep them in. Most chameleons will not leave their free range anyway if it has everything they need/want.
- The table thing also helps with drainage, I think. I've had my free ranges set up on custom-built tables that would funnel the water down and into a bucket, to drain later. So then I could run the mistking for a long time during the day and not get the carpet wet.
The lights you can hang from the ceiling, you can make plants taller by putting them on plant stands, and then feed by hand. I think that's all I can think of right now to consider. I had all 6 chameleons in the same apartment with a dog, and occasionally one would wander around the house, but it was never a problem. If you keep the house clutter-free it's pretty hard to miss a chameleon walking across the floor. They would go back to their free ranges too when they wanted to, at the end of the day.
A big plus in this is that they're more mentally stimulated if they can wander. Which I think can go a long way, health-wise.