Yes, you are too young to start training formally at present. Vocational training for teachers is either at degree or post-graduate levels. You can apply to train at university to be a primary school teacher. However, you can use your time studying for A-levels to undertake work experience in a primary school, shadowing teachers. If you do some reading, visit any good bookshop and look in the education section for books on classroom observation so you will be able to ask the teachers sensible questions during your time in school. If you can undertake some voluntary work with young people during the holiday, perhaps on youth work projects, this will benefit you when you come to apply for your course. By the time you reach university, you can have gained lots of life-forming experiences that will be invaluable to you as a teacher. Don't fret that you can't start your course yet - turn it to your advantage.