Not specific to Imperators, my guess it isn't different for them, young peafowl in general go through the breeding motions from very young age. Male chicks can start trying to grab and mount others as young as a day old, complete breeding motions seem to happen with birds 3 months old or older(can start earlier or way later though). It appears to be a form of playing for them.
Some think it is dominance thing.. problem is individual males and females engage in it pretty frequently while others do it much less often. Birds clearly trying to show dominance show it in other ways too.. the pairs that "breed" together can be otherwise perfectly amiable, no bossing or pecking order between them.