When will Maitreya Buddha come according to the Manimekalai?

It is said that Manimekalai was written between A.D. 890 and 950 and is known to have praised the Buddha's Teaching, the Dharma, as the most perfect religion. But what it must say about Maithree Buddha is just heresay. It must be just based on information received from other people at that time, that one cannot adequately substantiate. I say this because Maithree Buddha’s name is mentioned ONLY ONCE in the ENTIRE TIPITAKA. It is ONLY mentioned in the Cakkavatti-Sihanada Sutta (DN 26; The Lion's Roar on the Turning of the Wheel). This is what Supreme Buddha had to say on this:

“Long before this day is going to pass and in that time of the people with an eighty-thousand-year life-span, there will arise in the world a Blessed One, an Arahant fully enlightened Buddha named Metteyya /Maithree, endowed with wisdom and conduct, a Well-farer, Knower of the worlds, incomparable Trainer of men to be tamed, Teacher of gods and humans, enlightened and blessed, just as I am now.”

Just compare the year 1616 of the Manimekalai with that of the 80,000 year life span of a person at the time of the next Buddha. Does it make any sense for a 80,000 year old person to be living in the year 1616? I know well that this answer will be deleted with the reasoning that this does not answer the OP’s specific question. It seems like satisfying the OP is more important that Stream Entry (the state of Sotapanna) for this site, and that’s the very reason that people like Yuttadhammo Thero stay away.

Well in getting back to the subject of 80,000 years, you may now wonder whether there would be enough food for all if people are to live for 80,000 years. But it will not be so, as even in the past Kalpas (Aeons) people have lived for that long as per Buddha. Buddha once said,

“Dear devotee, I am looking at 92 Kalpas (a long time) to the past right now. In all that time, no one had to face any destruction of their families as a result of offering their food.”

Currently average age of mankind (life expectancy) is about 65years. Gradually this life expectancy will go down till 10 years then again life expectancy will increase again. Maitreya (Metteyya), a bodhisatta currently residing in the Tusita heavens is the next Buddha due to appear. Some time in the far distant future, once the teachings of the current Buddha have long been forgotten, he will be reborn as a human being, rediscover the Four Noble Truths, and teach the Noble Eightfold Path once again.

Let's bear in mind that according to the sources referenced in the Wikipedia page Manimekalai, this book was written either before the 5th century CE, in the 6th century CE or latest 950 CE according to different experts.

Anne E. Monius is a Professor of South Asian Religions at Harvard University and "a historian of religion specializing in the religious traditions of India. Her research interests lie in examining the practices and products of literary culture to reconstruct the history of religions in South Asia." She wrote the book "Imagining a Place for Buddhism: Literary Culture and Religious Community in Tamil-Speaking South India".

She talks about the book Manimekalai and 1616 prediction in this book, for which you can find the excerpt here. Please pay attention to the last paragraph on page 94, and the next two pages.

Her best guess is that since the Buddhist calendar usually starts counting from the final passing (parinirvana) of the Buddha (also see this answer), this refers to the year 1616 on that calendar. She is not sure about how this number was derived.

From the Wikipedia page on the Buddha, the date of the passing away of the Buddha is given as either 483 BCE or 400 BCE. That puts 1616 at 1133 CE or 1216 CE. This is definitely centuries after the authorship of the Manimekalai. So, that's quite sensible. Prof. Monius stated that this is more specific and substantially earlier than the estimates given in the Pali sources, for the coming of the next Buddha.

According to accesstoinsight.org's page on the Chronology of Theravada Buddhism:

Year 1 of the Buddhist Era calendar is the year of the Buddha's Parinibbana (death and final release), which occurred in the Buddha's eightieth year (480 BCE according to the "historical" timeline; 544 BCE by tradition).

If we use 544 BCE as the year of the Buddha's parinirvana, then 1616 would be 1072 CE, which is still centuries after the authorship of the Manimekalai (if we assume that it was authored in the 6th century CE).

Also interesting is this excerpt from the book by Monius (on pages 95 - 96):

In fact, if one looks beyond, or more appropriately before, the Pali literature that obviously concerns itself with the future Buddha, scattered bits of evidence can be found to suggest that the Manimekalai was not alone in the sixth century in imagining the arrival of a living Buddha within centuries rather than billions of years. In the various renditions of the life of Buddhaghosa, for example, it is reported that the monks of the Mahavihara greeted the composition of the Visuddhimagga by crying out to its author, "Without doubt he is Metteyya!" (nissamsayam sa metteyo). Although such a statement might easily be interpreted, on the one hand, as hyperbolic praise, likening only rhetorically the genius of Buddhaghosa to the wisdom of the future Buddha, on the other hand, such an identification might well depend on the expectation, like that of the ascetics confused by the miraculous events accompanying Aputtiran's rebirth in the Manimekalai (xv.23-35), that Metteyya's arrival on earth can happen at any moment. Such scattered phrases are certainly difficult to evaluate. Much more interesting and potentially useful for the consideration of the Manimekalai's vision of the future, given the central place of the wondrous almsbowl, Amutacurapi, in the text, is a story told by the fifth-century Chinese pilgrim to India and Sri Lanka, Faxian (Fa-hsien), concerning the begging bowl of the Buddha and the coming of Metteyya/Maitreya to earth.

You can read on in the same section, the story of Faxian, and how he obtained the story of the Buddha's almsbowl from an Indian monk.

Monius writes further on pages 96 - 97:

Faxian's story of the Buddha's almsbowl and its intimate connection to the coming of Maitreya provides a potentially enlightening parallel to the narrative of the bowl and the coming of the Buddha found in the Manimekalai. Such a parallel, especially given the relative proximity to the time and place of the Manimekalai's composition, of Faxian and the Indian monk who tells the story at the Sri Lankan Mahavihara, may help to illumine the Tamil text's vision of the future and the community to form around the coming Buddha.

Based on this, I would guess that the Manimekalai is a literary work of fiction, based on Faxian's story that came not long before the authorship of the Manimekalai. While it is unknown how Manimekalai's author derived the number "1616", we can speculate that he intended his readers to look forward to the coming of the future Buddha within a few centuries, perhaps to motivate the Tamil-speaking Buddhist community at the time, and also to kindle the interest of the non-Buddhist Tamil-speaking people, in Buddhism.