There's nothing special about Ti in terms of frame longevity. These days it's more of an aesthetic/classic/exclusive/sentimental thing. Some people just like the look and simplicity of a fine hand-crafted Ti frame.
But if none of that emotional stuff appeals, or you simply want the best in modern frame technology, then CF is the way to go. No reason why a CF bike can't last a lifetime too.
With my engineering hat on I would say that a well designed CF frame would more than likely outlast a welded Ti frame. But both should last for decades if well maintained.