@bopper is 100% right. Music is something you do because you love it, not because other people want you to or because it looks good.
If you do indeed love it, then there’s nothing wrong with starting “late.” I don’t know how it is at your school, but you can take concert band (band class) without having to do marching band. There’s nothing wrong with not doing marching band; it’s a huge time commitment and it can seriously wipe you out because of how physically (and mentally) taxing it is. You might be pressed for sleep and it’ll be difficult to keep up with your classes. I don’t mean to scare you, but I want to give you a clear picture of what marching band is like (because I didn’t get one and it killed me my first year). Your band is probably very rigorous too, if it really is one of the best. However, marching band can be very rewarding when you attend competitions and you get to see how much your hard work pays off.
Concert band/band class is significantly less time consuming (at my school anyway). You just have it like a normal class and you’re expected to practice and whatnot, and you’ll periodically have concerts. There’s no physical exhaustion involved and it’s much more relaxed than marching band. If you’re not interested in physical effort, then I strongly recommend taking band class at least. It’ll still be beneficial for you.
It will look good because it showed YOU had interest to join. Due to personal reasons I quit after 2 years, but as for your situation, I’d definitely encourage you join if you want to.