they will have the feeling of being independent and free.
Whereas this couldn't possibly happen to 18 year-olds just leaving high school and having the freedom of being away from parental supervision for the first time?
As soon as they sit behind the wheel, they tend to show off and speed up. This is particularly true of young men. They are prone to take risks.
This is a stronger point. Do some research and quote researchers who have shown that teenagers are biologically programmed to take more risks than older people (it's not just a matter of experience).
"Statistics have shown that teenagers have a higher chance of accidents." So what are the numbers for other age groups (you only talk about teenagers in the rest of the paragraph) If you look at other countries with a higher driving age, do you find that the youngest legal group of drivers still has the highest accident rate (in other words, are new drivers going to be the most accident prone regardless of what age they start driving).
These criticisms are all valid, but they are only part of the story. After reading the statistics and the reasons, there is no intelligent person who will agree with these criticisms.
They aren't good criticisms, though. See my comments on your other points for how the other side might try to counter you. Also, you can't say that the criticisms are valid, but that no intelligent person would agree with them, unless you believe you are unintelligent. Besides, you shouldn't be insulting people who disagree with you, as they are the people you are trying to persuade, and few people are persuaded by being called stupid.
The state of New Jersey recently raised the minimum age for getting a license from 16 to 17 and, if I am recalling recent news stories about the anniversary of this change correctly,
Make sure to double check the statistics, though. If the only reduction has been in the number of 16 year-olds involved in car accidents, then the numbers won't be very convincing. Also, if the numbers are looking at teenager driving accidents only, you'll run into a variation of the same problem. The overall accident rate has to have declined, as a percentage of the driving population. This may actually be the case, but you should make sure -- reporters aren't noted for their grasp of statistics.