I am with you Lidia, even though my Josey is only 14 months old, she is allowed on my shoulder. She has never bitten me and as long as she behaves herself and comes down when I ask I will allow her there. She does not spend a lot of time there, maybe 15 min to half an hour a day is about it. Now my sun Conure, Sunny, spends hours a day on my shoulder, she just rides around with me whatever I am doing, sometimes coming down on my arm or on my chest hanging on to my shirt to see what I am doing and if she can get into whatever she can. I have never had a problem with her either, both of my birds are sweet little darlings.
Its just a personal preference and if you don't feel comfortable with your grey on your shoulder then by all means do not allow it there. I may pay one day for allowing her that priviledge but it is my decision and I will live with it. :)