What age of drivers are the riskiest according to the national highway traffic safety board

I believe the answer is:  between 16-21, also 65 and on up.

Drivers between the age 16-21 tend to have high chance of collision due to lack of experience in driving and being much more likely to drive under the influence.
For drivers age 65 or older, the high chance of collision is caused by weakening nervous system which make their response a lot slower compared to the younger ones.