I've always heard that grey hairs were a sign of wisdom, but while looking through Preaching from the Types and Metaphors of the Bible by Benjamin Keach I found an interesting application of grey hairs.

Hosea 7:9Strangers have devoured his strength, and he knoweth it not: yea, gray hairs are here and there upon him, yet he knoweth not.
See All... Strangers have devoured his strength, and he knoweth it not: yea, gray hairs are here and there upon him, yet he knoweth not.

1. "Grey hairs are a sign that a man's best days, his youthful days are gone:  so some Sins and judgments upon a people, are a sign that their best days are past away, that their youth and glory is departing."
2. "Grey hairs are a sign of old age:  so some Sins and judgments upon a people, show forth that they are old in wickedness."
3. "Grey hairs come oft-times by great grief.  Scaliger tells us of a young man, who through the extreme trouble of his spirit, was turned Grey in one night:  so the judgments and miseries of a people, because of their Sins, make them Grey-Headed, and thereby look old and withered, &c."

These are just a few, Keach has more but I will leave you with these.