Flight feather problems

[Artist]

I have had my cocketiel for 15 years. The only time his wings were ever clipped was when he first came home from the breeder, 15 years ago. When I am at home, he is free to fly about. He is put back in his cage before I go to bed and covered. During the last few months, only one of his wings has flight feathers growing in, leaving him flightless. He has had some night frights, where he may have lost some feathers prematurely. But, by now, I would think they would have grown in. Any advice? Has anyone else experienced this?
Thanks:

 

[gracebowen]

The only experience I have is my baby. All of his tail feathers are gone. Every time a new one starts to come in he loses it. His previous owners clipped him very badly.He can't glide but he's getting stronger.

 

[MikeyTN]

Of he's having night fright, he may be knocking them out as they come in. Do you leave on a night light? If not you should.