The Collaborative International Dictionary of English v.0.48:

gray-haired \gray-haired\ gray-headed \gray-headed\adj.
   showing characteristics of age, especially having gray or
   white hair.

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

WordNet (r) 3.0 (2006):

gray-haired
    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]