Because you are only 18 I am gathering that you are talking about high school. Depends on your hours but I would probably wait, because if you have to do command time, theory and high school exams at the same time, you will probably at the expense of one, let the other one slide. So wait until you have finished school, until then build some command over the weekends or something. If you have got the command time well thats a start. If you havent done the CPL theory exams I would definetely wait, your brain will overload and you wont be at a disadvantage if you wait six months. There are many vairants and with the information you have given it is a bit hard to give you more advice. Post back and I might be able to advise you a bit more.