I first learned about the Metric System when I was in seventh grade, or, twelve years old. By that time, I had a good, solid, intuitive grasp of the SAE units and found it easy to understand how big things were based on those units. But as that was in the early '60s, I almost never encountered them outside of school for many years, meaning that I never had a chance when I was young to develop a similar intuitive grasp of the metric units. I've never had any problem working with metric measurements as they're logically defined but I still need to translate metric to SAE to feel confident that I know how long a distance is, or how heavy something is. Members of the current "younger generation" shouldn't have this problem, because they're learning and using metric measures right from the get go, and that's a good thing.