How odd must a person be in order to be diagnosed with a personality disorder?

How old. I assume u meant how old?. Personality do diagnoses are given above 18 years age.
Odd or Old? Dr. Ali answered if you meant "old" and not "odd." if you meant odd, the determination is based on the extent to which the oddness interferes with social relationships, family, work, and ability to actualize potential. Some people can be quite odd and yet have reasonably productive and happy lives.
Not necessarily odd. Depending in the specific cluster of pd, the person may come across as odd/eccentric (e.g. In paranoid, schizotypal or schizoid pers disorders), dramatic/emotional/erratic (e.g. In borderline pers disorder), or fearful/anxious (e.g. In avoidant pers disorder).