I always heard of the two second rule but I am not sure if that is law.
ten feet
Six car lengths is a good distance.
one car length
One car length for every 10 miles per hour.
1m
one car length per 10 miles per hour
it is recommende to keep a gap of at least two seconds behind the car in front of you so the distance varies with the speed
A safe distance, there is no defined limits of this type as driving near parked cars is situational (at best).
One car length for every 10 miles per hour of speed.
Do you mean when cars were first out? None. There was barely rules of the road and few cars. In Europe there were licences as early as 1880, but none list the legal driving age.
Know your distance between cars, fire hydrants and railroad crossing. These are the most over looked.
Cars are designed to be street legal.