The Collaborative International Dictionary of English v.0.48:

grey-headed \grey-headed\ adj.
   1. same as gray-headed.

   Syn: gray, grey, gray-haired, grey-haired, gray-headed, hoar,
        hoary.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

grey-headed
    adj 1: showing characteristics of age, especially having grey or
           white hair; "whose beard with age is hoar"-Coleridge;
           "nodded his hoary head" [syn: grey, gray, grey-
           haired, gray-haired, grey-headed, gray-headed,
           grizzly, hoar, hoary, white-haired]