They stay on for a long time.
People tend to stay quite a bit, and in fact, at the moment, we're experiencing a generational change. Shortly after World War II, the government paid for many veterans to go to law school, and many of those were hired in the late forties and early fifties, and they stayed until the 1970s and early 1980s, which is when we hired a whole bunch of new lawyers. Now those lawyers are all retiring at the same time.
One of the challenges we are facing right now is replacing the lawyers who are retiring, while continuing to provide our services.