'With nothing to do, no purpose in life, you'll just degrade, go to seed,' he said on Friday at a dialogue session at which he shared his experiences of active ageing with participants at the Silver Industry Conference and Exhibition (Sicex), held at Suntec Convention Centre.

The four-day conference, which ends on Sundaym explores ways to grow the seniors' market in Singapore and the region.

Mr Lee said that an active life, regular exercise and frequent travel were his secrets to ageing gracefully.

'I would not be able to speak to you in this way if I had not led a very active life, connected with many people throughout the world and tried to interpret it to make sense for Singapore,' said the elder statesman, who turns 85 this year.

'I'm determined that I will not, as long as I can, have my horizons slowed on me.'

He added: 'We got to educate those about to retire: Don't retire, work. Retirement means death.'

And he meant every word of it.

He said those who believed they could stop work at 55 to drink wine and play golf were 'done in'.

'Research has shown that those who lead a sedentary life tend to die quickly,' said MM Lee, who started jogging regularly in his 50s and now also keeps fit by swimming and cycling.

He maintains a packed schedule of international travel, including at least one official trip a year to regional powerhouses China and India.

The biggest punishment a man can receive, he said, is 'total isolation', which he defined as 'if you're not interested in the world and if the world is not interested in you'.

'If the mindset is that I'll reach retirement at age 62, I'm old, I can't work anymore, I don't have to work, I just sit back, now is the time I enjoy life, I think you're making the biggest mistake of your life,' he said.

'After one month...two months, even if you go travelling with nothing to do, with no purpose in life, you would get degraded, you go to seed. The human being needs a challenge.'

MM Lee also defended the Central Provident Fund scheme and argued against pensions for the elderly, which have to be supported by tax revenues.

The CPF scheme, he said, helps Singapore to remain competitive, as it aims for 'minimum tax rates and maximum self-sufficiency'.

'This way you are not passing the burden (of caring for the elderly) to the next generation,' he added.