There are alternative solutions to stopping people driving due to age relation conditions. A middle lane reserved for OAP's on motorways for example.
I would overhault the motorway network with an electrified inside lane for HGV use, middle lane for OAP use and the outside of the four lanes for 60-70 year olds to enjoy before they reach the age of 70.
Personally, I would give the vote to 15-16 year olds but the the weight of the individual vote would taper off after 70.
I really should be in politics - all those difficult decisions the current breed of politicians are too scared to take or implement!