During summer call the school district where you attended school and ask if they are having any art classes. If they don't, many community colleges offer art classes that people your age can attend. If you aren't finding local community colleges, look for private learning institutions. In Northern California there is one called "The Learning Exchange". In your area there might be different organizations which teach a variety of classes. Look for their class lists in libraries, art/crafts stores (which will also offer classes) and other places. Ask around where you live, someone will know where to find them.