Prophecies of the 10000 Years Golden Age.

Srila Prabhupada was frequently speaking about a golden age of 10,000 years, that started with the advent of Mahaprabhu. In his purport to SB 8.5.23, for example, he wrote:

“When Sri Caitanya Mahaprabhu appeared, He ushered in the era for the sankirtana movement. It is also said that for ten thousand years this era will continue. This means that simply by accepting the sankirtana movement and chanting the Hare Krsna maha-mantra, the fallen souls of this Kali-yuga will be delivered. After the Battle of Kuruksetra, at which Bhagavad-gita was spoken, Kali-yuga continues for 432,000 years, of which only 5,000 years have passed. Thus there is still a balance of 427,000 years to come. Of these 427,000 years, the 10,000 years of the sankirtana movement inaugurated by Sri Caitanya Mahaprabhu 500 years ago provide the opportunity for the fallen souls of Kali-yuga to take to the Krsna consciousness movement, chant the Hare Krsna maha-mantra and thus be delivered from the clutches of material existence and return home, back to Godhead.”

This period of 10,000 years is mentioned in the prophecies of the Brahma-vaivarta Purana. In the 129th chapter of part 4, there is a conversation between Krsna and Mother Ganga. The Lord is returning to His abode and mother Ganga is raising her concerns:

“Ganges said: O protector, Supreme enjoyer, on your departure for the perfect abode, Goloka, thereafter what will be my situation in the age of kali?

The blessed Lord said: On the earth 5,000 years of kali will be sinful and sinners will deposit their sins in you by bathing. Thereafter by the sight and touch of those who worship me by my mantra, all those sins will be burnt. There will be chanting of the name of Hari and reading of the [Bhagavata] Purana. Reaching such a place, attentively hear.
Sinful reactions including the killing of a brahmana can be nullified by hearing the Purana and chanting of the names of Hari in the manner of devotees. Just as dry grass is burnt by fire, by the embrace of My devotees all sins are burnt. O Ganges, the whole planet will become a pilgrimage sight by the presence of My devotees, even though it had been sinful. In the body of my devotees remains eternally [the purifier]. Mother earth becomes pure by the dust of the feet of my devotees. It will be the same in the case of pilgrimage sights and the whole world. Those intelligent worshipers of my mantra who partake My remnants will purify everything.
They are more dear to Me than My life, who everyday meditate only on Me. The air and fire become pure simply even by their indirect touch. For 10,000 years of kali such devotees of mine will fill the whole planet. After the departure of My devotees there will only be one varna [outcaste]. Devoid of My devotees, the earth will be shackled by kali. Saying this Krishna departed.” (Brahma-vaivarta Purana 4.129.49-60)

There is, however, some controversy about this golden age of 10,000 years, even amongst Vaishnavas. The verses 4.129.49-60 from the Brahma-vaivarta Purana can be translated in slightly different ways, that gives a different meaning. It can be understood that Krsna is saying that there will be devotees for the first 10,000 years of Kali-yuga and that mother Ganga should stay for the first 5,000 years after His disappearance. There are also two verses in the 90th chapter of the Brahma-vaivarta Purana, that state:

“Lord Hari will stay on this earth for ten thousand years of Kali-yuga and along with Him the Puranas, scriptures, and the worship of the demigods will also be present for that duration on this earth. For half that period the Ganga, other holy places, the village temples, and the study of Vedas by learned brahmanas will be present.” (Brahma-vaivarta Purana 4.90.32-33)

Source : https://thepathofbhakti.com/prophecies-of-the-golden-age/#:~:text=This%20period%20of%2010%2C000%20years,between%20Krsna%20and%20Mother%20Ganga 

According to Puranic sources,^[a] Krishna's death marked the end of Dvapara Yuga and the start of Kali Yuga, which is dated to 17/18 February 3102 BCE.^[9][10] Lasting for 432,000 years (1,200 divine years), Kali Yuga began 5,125 years ago and has 426,875 years left as of 2024 CE.^[11][12][13] Kali Yuga will end in the year 428,899 CE.

A dialogue between Krishna and Ganga (goddess) found in the Brahma Vaivarta Purana describes that for the first 10,000 years of Kali Yuga, the ill effects of Kali Yuga will be reduced due to the presence of bhakti yogis and the ability to nullify sinful reactions, after which Earth will be devoid of devout religious people and be shackled by Kali Yuga.

https://en.wikipedia.org/wiki/Kali_Yuga