They could possibly be some unaccompanied minors boarding before you, as well as some medical preboards. They will all be placed in the front rows. Then, any full fare/business class fare people will board in the A1-15 spots. If there aren't any in that group, you will only 2 people in line before you...A16 and A17.
The only seats you can't take are the exit row seats...you can't be under 15 for those seats. You also can't be flying with anyone that is under 15 and take those seats...so they are out for you.
Other than that.....you have the whole plane to choose from. I would choose seats toward the front...that way, you are in the first group to get off, and you will have plenty of overhead bin storage.