How long should I wait to paint my newly built house?

The most important thing to take into account is that everything should have dried thoroughly. Usually, drying takes up to four months for plaster, but it's recommended to wait one year to start painting it. 

In case you're wondering if your walls and/or ceilings are dry enough, there's a simple test you can do:

Cut out a piece of plastic from some packaging. Stick it to the wall, sealing the edges well with tape. Do you see condensation between the wall and the plastic after some time? That means your walls aren't sufficiently dry. If the plastic remains dry, you should be good to start painting.