What makes a voice get quavery and "old"?

Dear MA and the elves:

What causes the quavery "old" sound of some elderly people's voices? And is there anything I can do to prevent it in my voice as I age?

-- Toni, the net

Encased in our flexible, tubular larynx are cartilage and muscle that control the opening and closing of our very elastic vocal folds, the things that vibrate to make sound. We worry about our visible sagging, never realizing that our vocal folds get weak and saggy too. Voice muscles lose tone, while cartilage and voice box (larynx) stiffen. It all adds up to increasingly poor vocal control. Weak lung function may contribute too. So the experts say: don't smoke; drink lots of water; don't scream and yell; don't talk incessantly. Good advice for anyone.