Ответы
вот, написал все сам, читай, редактируй
Dear Mr. Johnson, I saw your advertisement in a magazine and I am interested in volunteering for a summer camp. I am 16 years old (или сколько тебе) and I fit your age requirement. My teachers say that I know English perfectly well, so I can help you. I am good at finding a common language with my classmates and younger children, and I have experience in working with them. My school organized assistance to kindergartens once, and I was one of the best helpers, so I will be happy to work for children with learning disabilities.
My family and classmates consider me hardworking, patient, and always ready to help. I would really like to try something new, I have good organizational skills, which means I am a great employer for you.
You can contact me at any time, I would be very grateful if you would consider me as a volunteer. I send you my application form and phone number for communication. I look forward to your answer.
With respect, (и свое имя и фамилию)