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Yes, it is both age and sex discriminatory, though I doubt that your use of the term will get you into Wormwood Scrubs. However, I suggest that you ask your colleagues at work if they object to you addressing them in this way. If they are comfortable with it, fine. But if someone does object, then you really must try to change. Why not address them by name? We all like the sound of our own name and it does project warmth and sincerity.