Little brother, navigating high school can be quite tricky. I hope these tips help because I really want you to hear them.
1. Keep pursuing academic excellence.
I'm so proud of you for earning straight A's in middle school and taking advanced classes. Keep up the hard work. Don't get tired of studying and doing homework even if your classmates have stopped. You have a strong work ethic and maintaining it will only benefit you when you enter college and the work force.
2. Don't let yourself be defined by numbers.
Don't let yourself be defined by your height, weight, football stats, GPA, or ACT score. Choose to be defined by your identity in Jesus.
3. Be as involved as possible.
You're already doing a terrific job being involved in extra-curricular activities and youth group. You may feel overwhelmed and like you are being pulled in too many different directions, but stay involved. This doesn't mean that you have to be involved in everything. Find a few groups and organizations that you enjoy the most and commit to those. Build friendships, gain experience, and become a leader. Whatever you do, don't completely quit being involved.
4. Tenacity is essential.
There will be times when you are tempted to give up and quit something you were originally looking forward to doing. I'm guessing that this will happen mostly with football but I'm going to use speech and debate as an example instead. In speech, you may go through periods where you want to change categories or stop competing altogether. Exploration at first is fine, but if you change categories every year you will never develop the specific skills necessary to do exceptionally well in any one category. Take it from someone who knows. This is where being tenacious comes in handy. Commit to a single category, practice every day, and be proud of the end result. I'm sure this applies to football somehow.
5. Learn to budget your money.
Mom and Dad probably won't make you work while you're in high school because they're awesome enough to cover gas money and allow you to focus on schoolwork. However, you may want to earn some extra cash over the summer so you can start saving for the future, take your girlfriend on a date every once in a while, and just have more independence. The truth is that money doesn't grow on trees. Mom and Dad don't have an endless supply of it. Track what you spend your (their) money on and make sure it's worthwhile. Create a budget so you can plan out where the money is going to go. The spending and saving habits you develop while you are young will be the ones you use as you grow up.
6. Treat your girlfriend right.
Remind her that she is beautiful, have fun together, and don't be afraid to splurge on cute stuffed animals. Always respect her and make sure she knows you will do your fair share of the work. You don't always have to win and you don't always have to prove that you are right. Make sure she feels safe so she can take risks.
Have a great freshman year and I cannot wait to see the young man you become.