A couple people have asked, "Why worry about it? Let them mature a bit, save money on insurance, and so forth."
Here's the issue in my mind: If they put off learning to drive 'til they're 17 or 18, they'll go away to college with very little driving experience -- perhaps less than a year's experience. Chances are good that my girls'll choose colleges that're 2-4 hours away. I don't think they'll have cars as freshmen, but eventually they will drive to college; I know that my oldest will need a car by the time she's a junior so she can do student nursing. If they don't learn NOW while they're living in my house with me, when will they learn? I don't mean learning the basic-basics of how to turn the car on, which foot petal is the brake, etc. I mean, if they don't learn now, when will they have the opportunity for lots of practice time with a parent? I don't want one of their college friends supervising them in learning to drive. And I don't want a brand-new driver going back and forth on the interstate, driving in a new city (after dark), and so forth. I don't think the extra year of maturity will "make up for" the lack of experience and practice behind the wheel.
My oldest was VERY EXCITED to learn to drive, and I have no doubt that my youngest will follow her sister's lead. If they didn't feel this way, I'd push them. I want them to have LOTS of time to practice driving around town with me.
One unexpected benefit of being a teacher: My oldest is getting more driver's practice than her friends. She drives me to school every morning, drives me home every afternoon, drives us around for any afternoon errands. I didn't see this perk coming, but it is really helping my daughter. Her driving skills are progressing well -- better than most of her friends.