It actually varies on the situation for Game Play. If I'm playing Metro's Challenges, I will play on Long because the rules state that the lifespan must be set to long. If I'm doing a Dynasty, I stay with the default settings. For Single Sims Aging and Story Progression are both off, because they go together like peanut butter and jelly, and I like to keep everything as is. If I play with a premade family, I simply like to keep aging on and play around with the sliders in the Game Settings.
This Christmas, when I finally get Pets for Sims 3, I will be writing a story about a premade townie specifically, and due to her elderly status, aging will be turned off.