I play rotation and I usually have aging turned off. What I normally do is use seasons to track the passage of time.
All my merfolk and vampires are immortal. It's a play on the beauty of eternal youth for merfolk. I'm a bit upset that immortals of different generations can't all be young adults.
Anyways, I age my sims manually. After reading this thread, I might age sims up if their rotation falls on the winter season.
Teens will probably get aged up if I decide that it's time. When Teens age up, that's when character values turn into special traits.