I know this is an older post, but for my baby linnies and parrotlets, I tend to have them in 30x18x18 cages until they get a little bigger, around six months of age. I don't know about others, but mine tend to be a bit clumsy! Then I move them into a small aiviary with lots of ladders, bongs, and swings as their wings are clipped. My linnies are moving tomorrow. My parotlet is still pretty small, he's a month younger then the linnies, so I'm keeping him in the breeding cage for a little while. They do spend time outside their cages, and they have perches, toys and bongs attached on the outside of their cage as well.
Debbie