John Paul also used his birthday Mass to stress one of the hallmarks of his 25-year papacy, elevating two Poles and two Italians to sainthood before tens of thousands of people gathered under a brilliant spring sun in St. Peter's Square.
Thousands of John Paul's own countrymen made a "national pilgrimage" to Rome for the birthday and canonization ceremony, waving handkerchiefs, cheering Poland's favorite son and joining the crowd for an occasional "Happy Birthday."
John Paul, who has repeatedly brushed aside suggestions he would step down because of his ailments, did so again after acknowledging birthday greetings from around the world.
He asked for people to continue to pray for him so he could "faithfully carry out the mission that the Lord has entrusted to me."
The Poles in the crowd responded with "Stolat," a traditional Polish toast meaning "May you live 100 years."
John Paul appeared in good form and spirits during the 2 1/2-hour service and spoke in a strong voice as he sat on the altar in front of St. Peter's Basilica in a hydraulic chair that allows him to celebrate Mass while seated.
His newfound vigor was in sharp contrast to his birthday celebrations a year ago, when an ailing John Paul struggled to read a few lines of his speech before turning it over to an aide to finish.
At that time, two prominent Vatican officials said they thought the pope would retire if his frail health deteriorated to the point where he no longer could govern his Church.
On Sunday, John Paul held up the four new saints as models for today's Christians, quoting one as saying "no condition or age can be considered an obstacle to a perfect life."
John Paul received birthday greetings in Latin from one of his closest advisers, Cardinal Joseph Ratzinger, who said he was expressing the gratitude of "innumerable people from around the world, well beyond the confines of the Catholic Church, even outside the Christian world."
Seated in a VIP area in the square were members of Italy's former royal family, visiting Rome after a half-century of exile.
Italian media noted something of a protocol gaffe on the part Marina Doria, wife of Victor Emmanuel, son of Italy's last king. She wore white, which under Church protocol is reserved for reigning queens.
Also attending the ceremony was a large Polish delegation, including the country's president, Aleksander Kwasniewski, and leading officials of Poland's powerful Roman Catholic Church.
After the ceremony, John Paul held a private luncheon with his top aides and the head of the Polish Church, Cardinal Jozef Glemp. The rest of the Polish delegation, including the president, lunched at a restaurant on top of the Vatican garage.
The birthday celebration was one of a series of milestones for John Paul, who recently became the fourth longest-serving pope in history. A visit to Croatia next month will be his 100th foreign tour, while the Church is preparing to mark his 25th anniversary as pontiff on Oct. 16.
On Saturday, a top Vatican official acknowledged what many observers have long suspected -- that John Paul suffers from Parkinson's disease. Cardinal Giovanni Battista Re, head of the Congregation of Bishops, said in a newspaper interview that prayer allows the pope to cope with the ailment.
The Vatican has never officially acknowledged the source of the pope's trembling hands and slurred speech, typical symptoms of the degenerative neurological disorder.
John Paul also suffers from crippling knee and hip ailments.
But he has appeared stronger in recent months. The Vatican attributes the improvement to rest and physical therapy, ruling any miracle cures.
With the four new saints proclaimed Sunday, all of them founders of religious orders, John Paul has now made 473 saints and is the greatest saint-maker in the Church's history.
The newest models for Christians are Jozef Sebastian Pelczar, a Polish bishop; Urszula Ledochowska, a Polish nun; Maria De Mattias, an Italian nun, and Virginia Centurione Bracelli, an Italian noblewoman.