It's been around for a long time. Think of the stereotypical medieval wizard or Greek philosopher. What does he always have? Bingo.

For most of human existence, listening to the people with grey hair (male and female) was the most reliable way of learning how to survive. They'd been there, done that, and lived to tell the tale.

It's only in recent history that things have started changing so fast that age==wisdom is no longer always true (though I think it still is more often true than some of the younger folks would like to believe).

Edit: a previous poster mentioned Gandalf. The Gandalf character wouldn't work nearly as well if he had a nose ring and a bunch of trendy facial tats, right?