“Live on the edge”
What is an edge?
An edge is the border of something.
A square table has four edges. If a small ball rolls across a table it will go over the “edge” and fall to the floor.
If you are at the top of a mountain and you walk along a ridge (with steep sides to the left and the right) you have to be very careful not to fall over the edge.
Someone who lives on the edge is a person who takes risks in their life. This a person who isn’t satisfied just doing the “normal” things that most people do.
When they are driving, biking, doing business, gambling, drinking, etc they take things to the limit to get extra stimulation.
John doesn’t worry about anything, he loves living on the edge. He’s always trying new things at work or at play. So far everything has gone fine for him and he has a great life. But I’m sure that one day he’ll have a serious problem.