I don't think age has anything to do with it Boo.
Phobias, by definition, defy rational explanation, so the 'well-meaning' comments like "Modern dentists don't hurt ..." and all that are meaningless. I was so bad, I couldn;t get through the front door of his building, never mind past reception, up the stairs, into the surgery, and into the chair ... without medication, so i sympathise totally.
i think if you spell it out from day one - including your presecription from your previous dentist, it will help him to help you. Good luck. I am off there myself today at 11:50 to have an abscess treated - let's compare notes after dinner.