That seems a fairly spurious argument, Steve. We can obviously never know what Beethoven may have produced in his 60s or 70s. Maybe great, maybe not.

Anyway, its beside the point. There are a multitude of people in a multitude of fields who made their greatest contributions at a fairly young age. Do we bemoan Einstein because his work on relativity was conducted in his 20s and 30s, and his later opposition to quantum theory subsequently disproved? Does that mean he wasn't a genius?

By the way, I don't think that Dylan is a genius, but I like his work well enough.