"Good Morning America's" Charlie Gibson, 62, is the heavy favorite to be the next anchor of "ABC World News Tonight," but one former colleague says youth should be served.

Gibson "is a very smart guy and the consummate professional," but ABC would do better with a younger person who can "grow into the job," says Bob Zelnick, chairman of the Department of Journalism at Boston University and an ABC staffer from 1977 to '98.

Gibson and "20/20's" Elizabeth Vargas, 43, among others, have been subbing for anchor Peter Jennings, who died Aug. 7 at age 67.

"If I were making the decision, I imagine Charlie would anchor for another five or six years," Zelnick, 65, says. With someone younger, "they could get a 20-year ride, assuming TV news lasts another 20 years."

Zelnick likes "World News Saturday" anchor Bob Woodruff, 44, and White House ace Terry Moran, 45, a possible successor for "Nightline" anchor Ted Koppel, 65. Vargas "is probably most valuable in her current role," Zelnick says.

With a younger anchor, ABC would "take a transitional hit" in the ratings, but it wouldn't be permanent, says Zelnick.

To be clear, naming Gibson (or Diane Sawyer, 59) "would not be a colossal blunder," in Zelnick's view.

"I like and admire Charlie. Do I think he has the weight to do the job? Yes. Do I think he's professional in every way? Yes. If this job started today and had a finishing point in five years, I'd pick Charlie. He's more mature in that particular seat."