You can start learning driving theory at any age....
Your first step should be to buy a copy of The Highway Code and familiarise yourself with it. It contains lots of advice for all road users and a section on driver theory. There are many other books and multi-media CD ROMs to help you learn the theory and hazard perception tests. The best people to give you personal advice about these tests are your driving instructor.
Apply for your theory and hazard test as soon as you start your driving lessons so that you have a date to work towards.
Remember, you can't apply for your practical test until you've passed the theory and hazard so it'll hold up the whole process if you wait too long.
You must bring along both parts of your provisional driving licence and some other acceptable proof of identity that bears your name, photograph and signature if you still have the old style paper licence.
Don't be afraid to contact a driving school before you are 17. We won't charge you for a friendly chat!
Once you've decided to learn to drive, you want to make sure that you reach test standard as quickly as possible and without taking more lessons than you need.
Take regular driving lessons whilst learning the theory and hazard test. This means your instructor can answer any questions you have about them and also help set it in the context of real driving.
Make sure you wear really comfortable clothes on the day of the test and go to the loo before you set out... And remember the examiner is only human (honestly!)
Most importantly... Good luck!