There's no "fastest way"
15 years of age. The fastest way to get it is by going to a private driving school rather than taken as a course in high school.
Go to school
An SR-71 Blackbird.
You can buy them or complete a lot of islands
school work
pick the fastest car you have, then just keep on going in the right direction.
The fastest way is going to Pakistan because you can get in to med school right after high school finish in four to five years and then you can intern how long you want to intern. This saves you four years.
I-75 SOUTH all the way crossing at the Ambassador Bridge.
On Interstate highway 90 East as the fastest driving route.
If you mean increasing the "driving skills" bar, then you can increase it by getting a slow moving car and driving it around at a slow rate of speed. Also doing the taxi missions or vigilante missions will help. The fastest and easiest way to boost your driving skills is to wait until San Fierro is unlocked and then go to the driving school (it's a requirement for the story line).
Theres only one way. Get at least a star in your driving rank on all 50cc Wii cups.
airplane is the fastest way!