Hormones?

For one thing, I think your baby is growing up. If he's showing mating behavior, then it's hormones, too. For starters, I would not let him on my shoulder for now. And it might help to work on hand control. If you don't already do some training with him regularly, I'd recommend it. It doesn't have to be very formal. Just start rewarding him when he is behaving, and ignoring him when he's not. You can work on the step up, even if he knows it perfectly well. Reward him when he does it when you ask. In fact, reward him any time he is behaving well, even if it is just verbal praise. It's positive reinforcement, and it works well, but if he is hormonal, you may not be able to make too much progress for now.

This is a good link for starting to understand biting behavior:
www.stfrancisanimalandbird.com/index.php/pet-resources/library/9-avian-care/84-my-parrot-bites-what-can-i-do

I'm afraid the hormones do ramp up every year, but you'll learn to read the signs and can adjust a little bit, at least. It's all very natural, and you're not going to eliminate it.

Do you cover him at night? The biggest clue to them that it's breeding season is lengthening daylight hours. If you can really block the light well enough to keep him on a 12/12 schedule, that will help. Also try not to touch him anywhere but on the head, neck, or feet when the hormones are up. Reduce or eliminate the warm and/or soft foods, especially from your hand. You can cut back a little on overall calories, and protein in particular. Nothing drastic. The example I was given was that if you feed him a higher protein version of his pellets, give him the lower. For me, that is going from something like 18% protein to 15%.

Parrots that are really unmanageable during the breeding season are sometimes given an annual injection of Lupron, but that isn't cheap, and it's not the first resort.

Check back, because you'll probably get some good advice from other forum members. 

Easttex has given you excellent advice here. It definitely sounds like your little one is growing up-- I'm sure there's a component of hormones, but also just testing boundaries. One thing you want to be careful not to do (as much as possible) is not react when you get bitten. Parrots have been known to bite simply because they find the reaction entertaining. They don't necessarily realize they are hurting you, nor that your response is a negative one-- they just know that you make a noise and move real quick when they bite you, and that's exciting. So, you need to clearly show them that this isn't going to lead to anything fun... but not by reacting and picking them up and caging them immediately, because that's another reaction, and you've given them your attention, albeit in a negative way, but that's still enough to reinforce the behavior.

So... Like Easttex said, when they aren't behaving, you ignore them. That is enough to send a message. It can take quite a while for this to sink in for these little ones, so be prepared to have to be patient. Another thing I do is use stern eye contact-- In my experience, particularly once the bird is familiar with your eyes, stern eye contact can definitely send a message in a way that words cannot.  I think this really only works if you are making pleasant eye contact with your bird on a regular basis, which, if you aren't, you should be   At any rate, this is a supplemental measure...  the main rule is-- reward good behavior, ignore bad behavior.

As far as how hormones develop over time, I think in a lot of cases they start out at their worst and get better over time. That might be the most typical way it goes... but hormones can fluctuate in birds just like in humans, and some will get more mellow over time, and others won't, and a few might get worse. It depends. It's simply a fact of life when it comes to having a bird. Personally, our QP, Cupcake (~5 yrs old), has thus far mellowed when it comes to hormones. She's never been a major biter, but she certainly used to bite more. Now, she rarely bites, and her springtime hormones seem less intense every year. Here's to hoping that trend continues My parents, however, have a cockatiel whose hormones were bad at first, but became completely out of control around the age of 9 or so... it was a huge problem for years... but now he is 25 and has mellowed out a lot.

Anyhow, most of the time, if handled properly, hormones are pretty manageable in the long run... but it takes time and patience to modify behavior-- so again, just be prepared for that. You'll get there. Feel free to ask any questions you have along the way. Good luck!