Assholishness and wisdom seem to be orthogonal to me. Most of us could probably name a dozen famous people off the tops of our heads who were both wise and unpleasant (most famously, Isaac Newton... arguably in the running for the smartest person who ever lived, but kind of a dick in his interpersonal relationships).

Old people have survived, which represents a first cut against doing foolish things, ranging from driving too fast to smoking to getting in bar fights. Barring cognitive decline, it makes perfect sense that older people should be, on average, more wise than younger ones. Plus some people do actually manage to learn a few things over the course of their lives. :-)