Old scientists are certainly capable of expanding and building on an existing paradigm, but they are very unlikely to revolutionize the whole paradigm.

I wonder how much of this is due to changes in personality and drive as life becomes a safe job, warm house, favorite chair and comfy slippers. With practice and purpose, could you keep an ability to revolutionize if you kept a real passion for it? From Daniel Dennett (parenthetical credited to Rodolfo Llinas):

The juvenile sea squirt wanders through the sea searching for a suitable rock or hunk of coral to cling to and make its home for life. For this task, it has a rudimentary nervous system. When it finds its spot and takes root, it doesn't need its brain anymore, so it eats it! (It's rather like getting tenure.)