Perhaps he wasn't in a way that would've kept him from innovating our industry but there's a thin line between knowing your purpose and becoming single-minded to the extent that you become stubborn and don't accept criticism or new ideas anymore. Steve Jobs showed some signs of that later in his life.
Besides, 56 certainly isn't old age, especially nowadays and even more so when your daily activity involves thinking about new product ideas that have the potential to change the world.
I see your point. I was kind of equivocating "being set in one's ways" with "being uncreative". Jobs was certainly single-minded throughout his life. In a way, he was set in his ways from an early age, at least in that sense.
Besides, 56 certainly isn't old age, especially nowadays and even more so when your daily activity involves thinking about new product ideas that have the potential to change the world.