People over 70 are more dangerous drivers than young people.
Firstly, the old people's reactions are much slower than younger one's. It's caused by aging and it's natural that younger people will react faster than people in their 70s.
Secondly, they cause traffic jams because of they are not willing to drive as fast as young drivers do, what makes people irritated.
Finally, old people make wrong choices more often because of many ilnesses they can suffer from.
To sum up, people over 70 are more dangerous mainly because of the aging process which makes them unable to react fast or make good choices.