Why? Because of compound interest.
When you save money, it earns interest.
The lump sum grows from interest being added every year or every month.
Interest added on top of that interest is known as "compound interest" - and means that the longer you save, the better off you are.
So people who leave it late - like Dave in the example above - have compounded their financial problems when it comes to cashing in their savings.
But it is worth remembering that pensions usually depend on the success of investments which, unlike savings, do not guarantee a set level of interest.

You've tried on a pair of jeans, quite liked them, but won't commit until you've visited three or four other shops. You then return to the first place and buy those jeans, having wasted the best part of an hour.
Palermo owner Maurizio Zamparini is that shopper and Beppe Iachini is that pair of jeans, having been re-hired on Monday, just three months after getting the boot.
Between 10 November and 15 February, the struggling Sicilian Serie A side brought in four other bosses before realising Iachini was their man all along.
"I return to Palermo with great enthusiasm for the good of the club, the team and the fans," said the returning coach.
Zamparini asked Palermo fans for forgiveness for "this month of chaos", adding that this had been because of his "wrong evaluation and misunderstanding" of Iachini.
Nowhere did the owner promise to give that trigger finger a rest though.
Palermo have failed to win any of their last four league matches and are 15th in Serie A, with 26 points from 25 games, four points clear of the drop zone.
Sacking and re-hiring managers in a single season is not unusual in Italy.
During the 2013-14 Serie A campaign, Catania ditched Rolando Maran who then returned, only to be sacked again.
Meanwhile, in the same season, Livorno dismissed Davide Nicola - the coach who led them to promotion the previous season.
Replacements Domenico Di Carlo and Attilio Perotti failed to make an impression, so Nicola was asked back again.

Police called to the collision on Long Street in Easingwold, North Yorkshire, found the white BMW 1 Series on top of a red Toyota Yaris.
A blue Vauxhall Corsa was also involved in the collision, which happened outside a terraced house near the Horseshoe pub at about 21:30 GMT on Tuesday.
The road was closed while the vehicle was recovered.
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Jade Barnes, who lives a few doors from the scene, said: "The house the car crashed into is the house of a heavily pregnant lady, so I went to check she was ok.
"We heard a crash but presumed it was people putting the bins out.
"It was only when I saw the emergency services that I knew something awful had happened."
Police said no one was injured and there were no arrests.
Saving a small amount of money regularly from when you start work will leave you better off than saving a bigger amount in later life.
[NEXT_CONCEPT]
We've all been there.
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A car has crashed into a house and on to the roof of another car.