I believe the answer is: 15-19 years old
The high number is caused by incompetent skills and driving under influence which seems more prevalent on this age group.
If put into a comparison, drivers within the age of 15-19 years old is 3 times more likely to be involved in an accident compared to the drivers that are 20 years old or older.
I would say it weakeneds because the graph is going to down to the weak point