What kind of electricians get paid the most?

Between sounds(low-voltage), residential, and industrial electricians, which one of them gets paid the most? Also, people say how many old man have you seen in this trade? So the question is how physical is the work and what kind of physical work is it? And what happens when they get old(about 50 yrs old) but still have bills to pay? Somebody on answers suggested that fiber-optics, fire alarms--which is low-voltage--is a good choice, is it true? Do they get paid more? Thanks!