The doctor in the OP is part of the problem. You don’t have to “focus” on it, but it’s important to bring it up. And kids/young people should really be encouraged to tackle it early since it’s much easier to make changes then.
I lost a significant amount of weight once between appts due to a lifestyle change. I actually had to bring it up to the doc who said that she had noticed it, but that patients often don’t like her to bring up the topic of weight. Um, what if I had lost that weight without changing anything? Seems like a highly medically relevant thing for her to at least to ask about.
My doctor didn’t say much about my weight gain, but he would hammer me about my blood work. He consistently told me that if I worked on my weight, my pre-diabetic status should improve to where I might not need medication for it. One year I finally took his advice, and dog gone it if he wasn’t right. Shedding those extra pounds has helped my blood work be at normal levels. No medications for me. I intend to keep it this way for as long as my body will allow me.