Jay, I think you're off to a great start! I like the look of your site. I know it's just a skeleton but was wondering if you were planning to hyperlink the Exercise, Healthy Eating and Motivation to actual pages when you're done. I just assumed they were links and I guess others will too.
Also many weight loss sites often emphasize similar tips so in your opening paragraph I would state why your site is going to be different and what it will do to help your readers. What are some of the things teens struggle with when it comes to weight loss (Not knowing what to eat? Teasing? etc.)
Get inside their heads and speak their language. That's the benefit of you actually being a part of the audience you target. Connect with them immediately by letting them know you understand their journey. You did that with your bio over on the side but it would also be great to emphasize that on the homepage.