When does knowledge become expertise?

 The other day I was talking with my father about something that was wrong with my vehicle and he told me how to fix it. He even said that he could fix it, if I got the new parts. I trust him 100% with my vehicle, but I had a revelation. Why? He has never been to mechanic school, nor has he read any books about my specific vehicle. He has just always worked on my family’s vehicles and so I came to trust him with mine. That led to the title’s question. When does knowledge become expertise? I think in this modern time we focus so much on education that we fail to realize that learning by doing was the way to learn things for centuries. And it’s not as if the base knowledge is going to lead to results. For instance, just because someone has taken the chemistry and knows the chemicals in a battery, doesn’t mean they could necessarily build one. Moreover, many people would answer the question by saying that if the person had learned enough that they could teach someone else then it is an expertise. But many people have problems relaying information further than their own minds (i.e. dyslexia or other such mental complexity). There are also those who say that age is a requirement for expertise in a subject. So, then what about the Doogie Howsers of the world. They are geniuses in their fields and could feasibly teach someone else. I think there is a middle ground for it all. Maybe a little education, being able to show someone else the knowledge, and certainly at least being able to apply the skill, if applicable, in the real world with your actual physical hands, but all within the thoughts that, no matter how young, anyone can become an expert on anything with enough fortitude, dedication, and practice. But that is just one man’s opinion. Thanks for listening to me ramble. I appreciate it. See you next time.