Um....Pullets roosting/pooping in nesting boxes...
My pullets hang out in the nesting boxes. I'm not sure if I should block them from the boxes until they're mature (they need to know where to go) but I don't want them to think they've been popping in there for as long as they can remember & will continue (therefore not lay in them when they are supposed to). Any thoughts? Thanks in advance.
This is a very common issue encountered with young birds. The easy answer is to do what you have suggested - block off access to the nest boxes until your birds are showing signs of being close to the point of lay. A nest sleeping habit can be hard to break - especially if allowed to continue - and poopy nest boxes are NOT good, especially when the eggs start coming.
The other thing to consider is whether your setup may be inadvertently making the nest boxes a preferable sleeping place to the intended roost spot - can you post a photo or two of the inside of your coop so that we can help you spot any potential pitfalls?