There are differences between the species and when they molt.
Mid to large Parrots commonly molt body feathers during nesting season and several months prior hormonal season so that they are in their best feather to interest their mate.
This same group will selectively molt flight feathers. Point being, they never want to be in a position of not being able to fly! As a result, they commonly molt two feathers from each wing. When those feathers are in place they will molt additional sets of flight feathers.
Age is very important as young Parrots are investing huge sums of energy growing and if they have recently completed flight feather replacement, they may not have the energy reserves to commit to extensive feather replacement.
It is very important to understand that the only signal the parrot has of a need to replace a flight feather is that the feather has fallen out or been pulled out. IMHO pulling flight feathers is dangerous as a bleeder may result. Pulling multiple feathers can place serious demands on their energy reserves.
Waiting for flight feathers to grow in is likened to watching (waiting) for water to boil. Soon enough, your beloved Parrot will suddenly fly.
