Kiwi I can not believe that you have a blue front Amazon that does not talk. THey are among the best. Have you tried one of those repeat boxes? I started salty with one of those and it seems to have done the trick to get him started. Now he picks up words on his own. You may want to look into one of those. he is a handsome devil regardless.
My Sydney is like Kiwi, he says "Hello" and "Buhbye" and he can do the full wolf whistle, but mostly just does the first half too! He's somewhere between 30 and 40 years old, and was neglected pretty bad, so he also might have been discouraged from talking.
My amazon pair that's about 18 years old also don't talk, and don't really make anything other than amazon noises. I've had them since October or so, so hopefully with some time they'll learn. Sydney I've had for a number of years now and I'd love him to talk, but he doesn't seem to want any part of it.
I guess it just goes back to the whole "not every parrot talks, even species known to be good talkers". My parents birds have never been mistreated in any way, but none of them talk. They make really beautiful and diverse vocalizations though. Even Alfie the G2 can make some really cute noises besides the screeching

. Lucy the DYH makes the most beautiful bird noises I've ever heard, almost melodic in nature and she vocalizes constantly. I think that's because she's wild caught and learned the noises they'd make in nature
I'm actually kind of glad Kiwi isn't a talker. I'd rather hear him make his goose honks and owl hoots than have him say "hello" and "pretty bird" over and over until I wanted to put my head through the wall. Our landlords IRN has a few phrases he knows (pretty bird, his name, hello, wold whistle etc...) and he uses them "often".
BTW- When Sydney makes the half wolf whistle, does he expect you to make the other half? Kiwi does! He gets real upset too if you don't. We use it sometimes when he's contact calling to communicate we're around.