What are your options for vet care? What are you noticing specifically in terms of possible sickness? His feathering does look a bit rough, as does his posture, but I am not sure what is normal for him.
Are you misting him in the morning? Never mist at night and make sure the temp is warm inside if you do (I tend to have it around 76-78 if spraying and then I dry quickly with a paper towel)
It just seems like those gray feathers aren't normal looking. Avian vet is 4 weeks out unless you pay a big emergency fee. We took the 'too once, but haven't ever taken Max.
How is diet, sleep etc? How often do you mist him?
Any hormonal behavior?
So, he has never been to the vet? You need to schedule, even if it is 4 weeks--that's what gives you a baseline for comparison if future issues arise. They need to go 1x a year and get blood a bare minimum of every 3 years. I know that is irritating, but it's super important for things like organ issues, dietary problems, etc etc. This goes for both parrots.
If things get worse or you see something obvious, I'd pay the emergency fee.
A very good habit is to weigh weekly. Use a digital kitchen scale weekly. Daily if health issues is suspected. 3% of body mass lost seek vet 5% or more is sick. Of course any symptoms should seek vet.
While over preening can be behavior when its legs and tail is usually a health issue, like yeast overgrown, kidney infection...sometimes can be sexual frustrated bird. But health issues need to be ruled out.