You must be 17 before you can start learning unless you are disabled or learning to drive a tractor or if you are applying to learn to ride a moped.
 
A D1 form is used to apply for a licence and this can be obtained from the Post Office. After you have completed it you must send it to the DVLA in Swansea together with the correct fee. The address to send it to is on the form. It can take between three to six weeks to process an application but you can send for a provisional licence any time after three months before your 17th birthday.

Full information about licensing requirements can be found in the Driving and Vehicle Licensing Agency (DVLA) leaflet D100 "What you need to know about driving licences" usually available from the Post Office.
 
You should wait until you receive your licence before you drive on the roads but, provided it is not restricted for any reason and your medical circumstances do not change, your licence is usually valid until your 70th birthday.
 
If you have any difficulty getting an application form for a provisional licence or if you need more information about driving licensing you can telephone the DVLA on 01792 772151 or 

visit their web page at www.dvla.gov.uk