What should I tell a 15-year-old NBA blogger?

That depends on what is goal is. He'd be better off regarding the writing as a hobby at this point, in which case the pontificating can have a point if he likes doing it and he feels it's worthwhile.

He's 15. It doesn't matter what he does right now he's going to be embarrassed about it in five years. Telling him "there's no point" is not constructive. Maybe tell him he needs to do some original research, learn as skill, interview, look at some stats and put them together interestingly. You guys seem focused on how the kid should be a beat writer... have you seen the other threads around here? What has he done to you to deserve this treatment?