To me, it all depends on the individual bird and your bond with that bird. Some birds are sweet, but just too unpredictable. Rarely though, you will have such a strong bond with your bird, you can trust them. Use common sense here, and know there is ALWAYS the risk of getting your ear or face bitten, which is something you have to accept if you do choose to allow your bird on your shoulder. Even the sweetest, most well behaved bird is still an animal. I grew up with large parrots, and there was only 1 of them (a female amazon I was particularly close to) who I would allow on my shoulder. Even then, I always knew there was a possibility she could bite, though she never did. I will not allow my 15 y/o rescue blue front on my shoulder, but my husband allows him up on his shoulder sometimes. Kiwi is a sweet bird, and has mellowed out a lot since we adopted him, but he was severely mistreated the first 10 years of his life, and I just feel he is too unpredictable to trust in a place of "dominance" near my eyes and ears. My husband is much more bonded to him, though I still think it's dangerous for him to allow him up there.
It sounds like you are not confident enough in your bird not to bite you to allow him on your shoulder at this point. Continue working with him to form a strong bond, and maybe in a few years, he will be trustworthy enough. And a better way to look at shoulder sitting is that it is a privilege that must be EARNED, and that some birds will just never earn the privilege, others can. Best of luck.