"Age shouldn't really be a factor," said Neil Duncan-Jordan, national officer at the National Pensioners Convention. "Many older people feel like second-class citizens because of their age in so many walks of life, including the leadership of political parties."
Duncan-Jordan raised concerns after Campbell's age was referred to by the media and by both his leadership opponents, Chris Huhne and Simon Hughes.
"There's no other section of society that could be portrayed in such a negative way," Duncan-Jordan said. "If you think about substituting another category for older - say women, gay or black - there would be massive national protest."
Bringing age into a political debate was unwise for a number of reasons, Duncan-Jordan said, not least because it alienated members within political parties' own ranks.
He said: "It's not clever to make age a public issue, otherwise we'd be writing off a whole swathe of politicians who are now over 65.
"That stands as true for the Tories and Labour too," he added.
Hughes alluded to Campbell's age at the launch of his manifesto, when he described himself as a leader for this generation and called the former Olympian a "caretaker". Huhne has also suggested that Campbell's age would cause the party to lose a leader "almost immediately", were he elected.