What is the exact Age Limit that Buddha can live? Does any one know what is the exact Age Limit that Buddha can live? i heard that one of previous Buddha lives His Life for 40,000 year.
A Buddha can live as long as he wants – even an aeon, as the Buddha potentially have the age or lifespan of an aeon.  – but this decision depends on the others. If an arahant that is closest to a Buddha makes a formal convincing request for a Buddha to live for many thousands of years, he will do so. But always the Mara gets in the way, and asks the Buddha to attain Parinibbhana, no sooner His Dispensation is fully established. In our Gautama Buddha’s time, this happened when he was 85 years of age. 

Buddha once said that anyone who had developed the Four Bases to Success (iddhi-pada), and is firmly rooted in these four bases, if he wishes, could live until ones full age - in our times until 100 - 120 years. Four bases to success (iddhi-pada) are Chanda Iddhipada (great desire to practice); Citta Iddhipada (Will); Viriya Iddhipada (effort or perseverance -repeatedly applying the mind); Vimansa Iddhipada (examination leading to insight).

The Buddha asked one of his ten chief disciples, Ananda, about this, once He knew that He has achieved the goal of fully establishing his dispensation. He asked not once or twice, but sixteen times. But every time Mara got in the way. Mara had power over Ananda, as he had not yet fully purified himself. So Ananda never heard what Buddha said, as he was not himself. And it was Mara who asked the Buddha, not Ananda. If Mara had not intervened, Ananda would have asked the Buddha to live a prolonged life, out of compassion for the world.

Mara appeared before the Buddha and reminded him of a promise the Buddha made to him forty-five years before, immediately after the enlightenment. At that time, Buddha said that he would not attain Parinibbhana until he had established and well taught the Doctrine. Now that had been accomplished, Mara said that it it was time to fulfill the promise. In reply The Buddha said that he would attain Parinibbhana in three months. A Buddha sees that this mortal body, with its six sense faculties, as belonging to Mara. This shows the detachment of an Arahant to the ways of this world. Buddha kept this body until the Dhamma was fully established, and as promised, and as invited by another, left this earth  than live a prolonged life.