That pic of him peeping around the door is most adorable! He will have you wrapped around his talons doing his bidding in no time at all.
With the new photos, I'm completely convinced he is a YNA now. I would imagine YNA's have subspecies much like the BFA's and DYH's though I am not familiar with YNA subspecies like I am DYH and BFAs. Someone else may have further insight. Though I will say, to my understanding, many YNA's do not have much yellow on their napes until they are mature birds and it spreads with age. 8 is just entering puberty and around the age (many) amazons colors start to spread being sexually mature birds.
BTW- Are you certain he's male? Hot 3 amazon, male, 8 years old and 'polite' do not typically go together in the same sentence
Edit: I think I've identified why he strikes me as a YNA, he has a deeper green color to the plumage (or at least the photos show that way). YCA's I am seeing photos of only appear to have brighter green plumage the any YNA I've seen. I am, of course, purely speculating for fun here but I do know some amazons do have a deeper green with a more blue overtone while others have a more 'lime' green color. I am also seeing a lighter, more mottled beak on YCAs than YNAs. Oh, and the black edges are normal for healthy amazon feathers. Almost makes them look scaly, like the big modern day dinobirds they are!