“If you are poor, you are not likely to live long,” he said at his village house in Eastern Cape province for a birthday interview.
He is expected to spend the day at home with his family.
His predecessor as president, FW de Klerk, described him as one of the greatest figures of the last century.
Mr Mandela was jailed for 27 years for his ANC activities but went on to become the country’s first black president in 1994.
Since stepping down in 1999, he has become South Africa’s highest-profile ambassador, campaigning against HIV/Aids and helping to secure his country’s right to host the 2010 football World Cup.
In 2004, at the age of 85, Mr Mandela retired from public life to spend more time with his family and friends and engage in “quiet reflection”.
On Friday, appearing before reporters, he said: “There are many people in South Africa who are rich and who can share those riches with those not so fortunate who have not been able to conquer poverty”.
In an earlier radio broadcast, he said he was honoured that people had chosen to celebrate the birthday “of a retired old man who no longer has power or influence”.
Tributes, gifts, banners
Mr de Klerk, who was awarded the 1993 Nobel Peace Prize along with Mr Mandela, said the former president was a born leader with the “assurance, the humility and the grace of a true natural aristocrat”.
|Mandela upon release|
|1918 – Born in the Eastern Cape
1964 – Sentenced to life for high treason
1990 – Freed from prison
1993 – Wins Nobel Peace Prize
1994 – Elected first black president
2004 – Retires from public life
2005 – Announces his son has died of an HIV/Aids-related illness
“After his inauguration, Nelson Mandela used his personal charm to promotereconciliation and to mould our widely diverse communities into an emerging multicultural nation,” the last president of the apartheid era told reporters on Thursday.
“This, I believe, will be seen as his greatest legacy.”
Friday also marks 10 years since Mr Mandela married his third wife, Graca Machel.
“He is simply a wonderful husband… and we enjoy every single day as if it is the last day,” she told CNN.
Official birthday celebrations are due to be held on Saturday.
A school choir in Qunu has created a song especially for the former leader.
Mr Mandela raised funds to develop the Nkalane Junior Secondary School out of its original mud buildings and used to be a frequent visitor.
In other birthday events, reported by the South African Press Association.
Many of those who have worked with Nelson Mandela and had a close friendship with him over the years say that behind the adulation he inspires there is a very human and often extremely private figure, the BBC’s Mike Wooldridge reports.
Three generations reflect on Mandela
Fellow Robben Island prisoner Mac Maharaj told our correspondent Mr Mandela was truly an icon.
He reduced a veteran white police officer to tears on his inauguration day when he walked over to him, shook his hand and told him “today you have become our police”.
But Mr Maharaj argues that the event that sheds most light on Nelson Mandela’s character was the killing of the popular ANC leader Chris Hani in 1993.
Mr Maharaj believes that if Nelson Mandela had called for an insurrection in response it would have been unstoppable but, instead, he went on television to call for calm and commitment to democracy.
Action on behalf of justice is a constitutive dimension of the preaching of the gospel.
Justice in the World – 1971 Synod of Bishops