The 72-year-old Scots MP also suggested that politicians in their forties had not had enough time to build up valuable experience outside parliament.
Sir Menzies was forced to resign as leader of the LibDems in 2007 amid increasing speculation over his leadership, including over his age.
His replacement, current LibDem leader Nick Clegg, is 46, while Conservative leader David Cameron is 47.
In an interview Sir Menzies, who is retiring at the next General Election, warned that it was "very foolish" for parties to rely entirely on fortysomethings.
He said: "I think it's very, very foolish of political parties to think that the only way in which you can run a successful political system is to have 45-year-olds.
"It doesn't work. I was 46 (when I was elected). I'd done about 18 years at the bar ... I prosecuted serious crime, I defended serious crime.
"I did a lot of matrimonial work in the early days.
"By doing that, one had a pretty good idea of the kind of stresses and strains which people have to face in their daily lives."
Sir Menzies also stressed the benefits of older MPs.
He said: "(More senior MPs) give a depth of, if you like, corporate knowledge for Parliament."
In the wide-ranging interview, with Total Politics magazine, the Fife MP also warned David Cameron and Nick Clegg not to end the Tory-LibDem Government "at each other's throats".
A descent into bitterness and recrimination would damage both parties and the prospects for future coalitions, he said.
With less than 18 months until the next General Election, both parties are increasingly trying to highlight their differences.
Only last month Mr Cameron joked that he kept a "little black book" of policies the LibDems would not let him implement.
Sir Menzies called on the party leaders to set up a group of six "wise men and women", made up of backbench MPs from both parties, who could agree the terms of the separation.
The outcome would be binding on all sides.
Sir Menzies admitted that the idea had, so far, gained "no traction".
But he said it was important to have a "dignified, non-acrimonious" end to the Coalition.
He added: "The ministers will have to keep going to the very end. Why? Because the country has to be governed.
"But I think we should accept that the point's going to come at which politically ... we're going to start - well it's started with differentiation - moving away from each other.
"And we should do that without recrimination or acrimony or intimidation or anything of that kind.
"Why? Because it is very damaging for both parties if it breaks up in a row, or a series of rows.
"But more to the point, it would have a considerable impact on the creditability of coalition.
Sir Menzies also said he spoke to former Labour leader Gordon Brown five times during the Lib-Lab coalition talks in 2010.
"He was so keen to try and see if it couldn't be made to work," he said,
"But elsewhere in the Labour Party, people were taking a different view altogether. There were people like David Blunkett and John Reid, important people in the Labour Party, whose view very firmly was to go into opposition.
He also explained why he was retiring, and insisted that he was not abandoning politics just because he would no longer be an MP. "I was very, very concerned about was that I should not appear to be someone who is just hanging on, as it were, and no longer able to do all the things I'm able to do at the moment," he said.