Wow. This is a subject that is near and dear to my heart.
Before retiring as a police officer, I received specialized child safety seat training. I have seldom encountered a subject in which lay people were less knowledgeable.
If you had seen the videos that I've seen, and/or been to the fatal traffic collisions that I've been to, you would understand that parents who love their children, should not be attempting to justify turning their children forward facing as soon as possible- they'd be keeping their children rear facing AS LONG AS POSSIBLE.
Not as long as convenient, not as long as your spouse wants, not as long as the child appears to want to...AS LONG AS POSSIBLE.
An equally important issue, is that in all of the child safety seat inspection clinics that I've participated in, I have NEVER seen a single child safety seat installed correctly. And even the smallest error, can render the child safety seat virtually useless. The child safety seat manual and the vehicle owner's manual are written in plain English- just READ them, instead of just guessing. Your child's life hangs in the balance...