I agree with goodman. The age isn't exactly the most important thing... it just depends on each person's maturity and responsibility level, as well as their own driving skills.
There's some real s***heads that even at the age of 35 still drive like crazy #$#$%@#%
When there's other younger guys who actually are quite cautious while driving.
It's just a matter caution and patience. But teenagers tend to be real stupid in this country, so.... there's the consequences.