Normally, for car drivers, the earliest date your provisional licence can become valid is your 17th birthday, however you can apply for the licence up to three months before your 17th birthday.
That is if you will be driving a car or motorcycle. You can drive the following vehicles at 16.
Mopeds
Small invalid carriages
Mowing machines
Some agricultural tractors
Some small cars or vans if in receipt of a Mobility Allowance