Honestly, it sounds like he's just wanting to be with you more often...It could very well be that he's a bit more hormonal this year than he has been in past years, that's perfectly normal, as some years are worse than others, and that could be a part of it just as Noodles stated above...However, as you know they are extremely intelligent, about the level of a 3-4 year-old human toddler, and they are also "Flock Animals" innately. So it's not unusual at all for them to follow their "Flock" when they go somewhere and want to be with them all the time...And you and everyone else who lives in his house are his "Flock"...
He's only 21 years old, not at all old for an Amazon, and as I said, they are totally and completely "Flock Animals", and you and the others who live in your home are literally his "Flock", as other Amazons would be in the wild...You've had him since 2001, and while that seems like a very long time to us, to them it's not long at all when it comes to forming relationships and strong bonds with us. Sometimes Amazons actually take a full 21 years or more to allow their people to even touch them. I know of someone who has a Yellow-Naped Amazon that his father brought home when he was only 9 years-old, and the Amazon was only 12 years old...Now the Amazon is 36 years old and the owner is 34 years-old, and he owns him solely, as his father has passed away. So this person has literally lived with this Amazon all those years and been "his person" all those year, and it's only been in the last 10 years that the bird will actually come to him when he's called, and only in the last 5 years that he's allowed him to hold him, pet him more than just on the beak, and give him kisses. He is now, after all those years, FINALLY trusting of him and finally bonded to him and now wants to be with him all the time, and on him all the time...And that all happened very gradually and slowly over the last 5 years!!!
So, if I had to guess, I'd say that your Amazon has been getting more and more trusting of you and more and more bonded to you over the years that you've had him, very very gradually over time, and he's now gotten to the point where he very much trusts you and considers you "his Flock" and "his person", and he's now gotten to the point where he simply wants to be with you and in your presence whenever you're home...This isn't a problem to be solved at all, it's just the natural progression of an Amazon forming a strong bond to it's person and actually considering them his Flockmate, and wanting to always be with them when they are home.
This isn't something that needs to be fixed or that you can "stop", in fact most Amazon owners desire this type of bond with their birds and would love to be in your place. You can see just how long it can take for an Amazon to form this kind of bond with it's person, and it's totally dependent on the individual bird on how long it will take...Very few Amazons that are re-homed and adopted by a second person will immediately trust and bond with them and think of them as their Flock or their mate; there are always exceptions, but usually that only happens when someone brings home a hand-raised, just-weaned baby bird...After they are re-homed by their original owners, they tend to become very untrusting and unwilling, and it can take years and years for them to form that kind of bond with a person again...Amazons in particular tend to work this way...So it's not a problem, there's nothing "wrong" with him, he just wants to be with you whenever you're home. How you handle that is up to you, but it's not a "problem", and if you take measures to try to "stop it", you could actually really ruin your relationship with him, depending on what exactly you do to try to stop it...
***I'd wait until you get through this spring into the summer, after breeding-season ends and his hormones will surely be calmed down, and if he's still acting this way or his "clingyness" progresses even more, then you'll know that this is simply his bond to you getting stronger and stronger over-time...It does seem counterintuitive to us for it to take literally decades to form a strong bond with someone, as humans tend to just pair-up with another human the minute we meet them, lol, but parrots just don't work that way, nor do many other animals. And with parrots being as intelligent as they are, and being the extremely social "Flock Animals" that they are, it can take literally years and years to decades for them to get closer and closer to their person or people...