I agree with Dave O. When we call someone an "old fart", it's not the "old" that we're focusing on.

On a serious note, I lost a relative to Alzheimers a few years back. She was only in her early fifties when the disease first became apparent, and took a very long time to develop, most of which she was corpus mentis, if increasingly forgetful. And that was before the newer treatments available. You'll be all right, Billy, keep smiling.