Has he been to the vet yet? Behavioral plucking in young birds is fairly uncommon, and really uncommon in budgies. So the fact that he is a young Budgie plucking is definitely a concern.
If it's medically related, there might not be a lot you can do until the underlying cause is determined and resolved.
Diet related would also fall under medical.
Behavioral is usually related to boredom. Giving toys for your bird to chew, foraging for food, plenty of access to flying, etc, can help alleviate plucking. If you consider that in the wild they have a flock, are flying, finding food, preening, and starting families as the bulk of their daily activities, when we bring them into our home, we need to make sure they have as many of those outlets as we feasibly can. When they get a cage and a bowl of food, and there's only preening left, some will overpreen until they damage their feathers.
There are plucking collars you can buy, so you can put it on their neck to hopefully block their ability to pluck, but they aren't foolproof and they are usually not meant for long term usage.
have a nice day further!
