Not everyone died before the age of 30 in cultures like the Hohokam, even though infant mortality was higher than in modern industrial nations, young men tended to die from violence or accidents, and young women faced risks from childbirth. But those who managed to survive their first three decades had a good chance of living to 70 or so. Archaeologist Christine Cave has an insightful explanation of how this could be so, based on her research into what she calls the "invisible elderly."
Those who did survive may have been treasured for their wisdom. In any case, that's how I prefer to think my Watermasters treated their elderly. Older people play important roles in all my books, as repositories of history and myth.
I had my mother teach me to read when I was four, and I've never stopped. Now I can play with words all day long... it's the best job in the world.