There is a ton of miss information about Primary and Secondary Wing Feathers and how long it really takes for them to be replaced.
Natural Wing Feather replacement 'depending on the Parrot' can take as little as a month to as long as five years. Since so much of feather replacement has to do with the available energy, i.e. the health of the Parrot and the quality of its diet. Because of their size and complexity, feathers of the Wings and Tail Feathers are expensive to replace (requires great stores of energy).
So, if we assume that the Parrot is in great health, and very low stress levels. The Parrot will replace one to two feather per Wing (or a total of two to four at a time). The process starts with that /those feathers becoming loose and falling out! This natural process would be on-going as the Parrot cycles out the older feathers first, then on to the next younger.
With very young Parrots this process can be slow to start, since near every feather is a fairly new feathers. The active flapping of your Parrot is driving two things: First, building /maintaining flight muscles and development of its Heart and Air Sacks. Second, a signal to the 'system' that flight is not possible and that Wing Feather replacement is needed.
It is very important to provide a very health diet, minimize stress and allow active Wing Flapping.