He is only 5 weeks old...haven't seen any feather picking from 2 others...
looks like one feather growing off the tip of another feather in several
places.
It could be one of the other two feather picking her tail feathers. I have one or two that look like that too and I know mine were feather picked. Feather picker was removed.
Two things appear to be going on. The first set of tail feathers are in process of being replaced by heavier more pigmented second set. The bird may also be getting feather trampled or pushed up against something while roosting / sleeping causing barbs to fray.