My older Labrador, now 6, has had a false pregnancy following every season. She was neutered last year because on a couple of occasions she showed signs of being unwell at about the point that the pups would have been due. The vet thought that it could have been the start of a pyometra but that I noticed subtle changes in her behaviour so it was caught and stopped very early on. Apparently womb infections are more common in bitches that have false pregnancies and hence we took the decision to have her spayed.
She never made nests or showed much change in behaviour but was full of milk for weeks! We never let her outdoors without us being there from as soon as she started her season so knew that she couldn't be in pup.
Our young bitch, now 15 months, has had 3 seasons already and one false pregnancy so far after her second season. Again no nest building but she was full of milk and quieter than normal.
So, yes, it happens in young bitches in our experience.