Here's my personal view on minors and sex, and I'll use this to guide myself through the storyline. I figure that once guys hit puberty, they're going to be sexually active. So the questions that I have to answer are this:
1. What is the fictional-story age range limit for a partner for a minor? Generally speaking, my rule is a maximum of 5 years older.
2. What kind of sexual activities should a guy under the age of 16 be involved in? Before that age, I can see guys involved in frottage, jacking-off (mutually, alone, with each other, all the time, etc.), body exploration ("If I put my finger here, does it feel good?"), and oral sex (blow jobs and rimming). If they are involved in actual f**king, it will be with another minor that is close in age to them.