The forty-something presidents are arriving, and not just at 1600 Pennsylvania Avenue. New chiefs at the University of North Carolina at Chapel Hill, Dartmouth College, Virginia Commonwealth University, and West Virginia University can't get their AARP cards yet. More are on the way. Fully 90 percent of presidents are at least 50 years old, according to statistics from the American Council on Education (ACE). Many incoming presidents will have a chance to leave their mark. Search committees are looking for candidates who are likely to stick around for a decade. Anything short of six years, and one really can't accomplish much. The average tenure for a president has grown to 8.5 years, ACE figures show. The reason is that stability pays. Presidents spend years steering complex projects and cultivating personal relationships with donors, lawmakers, and faculty members. A quick departure means starting over. One university chief who plans to stay in his post for at least a decade is Holden Thorp, who became chancellor of the University of North Carolina at Chapel Hill last summer. An alumnus and faculty member, Mr. Thorp is 44. Young presidents have the advantage of being able to serve long stints while still in the prime of their careers. They may also be better equipped to cope with the grueling demands of the job. The challenge for universities is holding onto a hotshot president. Edward H. Bersoff, the former head of Virginia Commonwealth's governing board, was chairman of the search committee that hired Michael Rao. After nine years as president of Central Michigan University, Mr. Rao, who is 42, has already led three universities of increasing size. Mr. Bersoff says it is naive for universities to think that they can keep a president for a decade. He wants Mr. Rao to make a difference at Virginia Commonwealth, which he knows will make him attractive to other institutions. One has to be realistic about it. If one gets a superstar, he's going to be in demand. But that won't be a problem for Mr. Thorp. He joined the North Carolina faculty in 1993, and had an impressive run as a professor of chemistry, including lucrative inventions relating to electronic DNA chips. He led the College of Arts and Sciences for two years before becoming chancellor. Even if other universities come calling, Chapel Hill is a good enough gig for him.