Maxing out early isn't something to be worried about. Slowly increase your mileage by 2.5 every other week during the summer and depending on your ceiling you shouldnt max out in high school.
Maxing out early isn't really something to be worried about. Your ceiling is your ceiling no training is gonna change that. Don´t do crazy mileage, no diets. Listen to your body, get a list of all things you need to consume throughout the day and make a checklist. If you do all that you can train aggressively and not get burnt out/injured.