While the elderly generally have slower reflexes, it would not be fair to keep a perfectly able person from driving solely based on their age. If they have medical problems that would prevent them from driving ( poor eyesight for example) then they shouldn't be able to drive, but one shouldn't be restricted based on age alone.
Not everyone that age has the same problems or the same magnitude of problems so denying them a license solely based on their age would be unfair. What would be fair would be to offer them an opportunity to retest. If they can pass another driving test they can keep driving.
Those who fail should be offered a stipend to use on taxis and buses so they can still remain sufficiently mobile.
Elderly people don't respond as quick to road hazards. This is also accompanied by poor vision. Poor vision can cause a person to not see a car coming in front of them or a kid crossing the street. On a show called brain games, they did a test where a 21 +/- year old and a 55+/- old were to drive on a course and avoid beach balls(road hazards) being thrown at their car. The 21 year old was able to avoid them better than the 55 year old and was also able to have better control of the car( driving through cones).
You can drive but there should be a limit. Most people when elderly people have chance of suffering form eye problems. Which can cause serious accidents. They can have Alzheimer and slow reflexes which mean they are a risk on the road. I mean what other way is there. I know it's a free country but everything has a limit.