Old Gray Beard

When John and I adopted Libbie they told us she was 2 years old. If that is true that would make her approximately 4 1/2 years old now. So, why on earth is she already going gray? At first we noticed just a few white hairs...now it seems to be growing exponentially and at this rate her whole head will be gray by the end of the summer...poor girl! Someone needs to hurry up and make a product for dogs like 'Just for Men' but for dogs.