You boy is coming of age :) This is totally natural behavior for him. He is now the eqivalent of a nasty teenager. He may be frustrated due to hormonal changes or the inability to breed, (yes, it does happen :) )
I am going to post a wonderful website that will walk you through how to get him to stop. I have used this on my bird...step by step...and it will work amazingly fast IF you follow it.
http://www.cockatielcottage.net/bite.html
I notice that you allow him to get up on your shoulder. Honestly...that is a no no...especially NOW. He is looking at you as you are benieth him. He is in charge (atleast that is the way he sees it)
The most important thing to remember is patience. One goofaw will set you back in his behavioral training. Slow and steady, in this case, wins the race :) Good luck and let me know if there is anything else I can help you with. If you found my answer helpful please remember to click the green accept button :)
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