According the Puranas themselves they are that old. It is only British Indologists who claim they are of recent origin, and they followed the Muslim invaders assesment of India, which is very biased. More recent scholarship is discovering a much more ancient time scale for not only Sanskrit but the entire Vedic culture.
There are descriptions in various Vedic texts of astronomical features that are incredibly ancient, described as viewed. One such stellar or planetary alignment has been found to be 26,000 years ago.
I will grant that it is pre-Roman, but whether it is even as old as Sumerians would take an amount of guesswork. Hope the Pakis leave something for future archeologists to dig up along the Indus. I suspect we don't know 1% of what could be known of those times, not even which aeon things belong to.
I agree with the British Indologists on that, not because of any Muslim assessment, but because I follow the empirical method and empirically we do not have any extant documents on Buddha's life which are that old. The extant copies of the Puranas date from between c. 400 BC and 1400 AD, and documents written after 400 BC are not and cannot be eyewitness sources on events from 3000 BC. Empirically we would need some sort of pre-Puranic evidence to support any traditions about Buddha being from 3000 BC. I am not aware of any such evidence. I am aware of the pre-Mohenjo-Daro find mentioned elsewhere in the thread, from previous discussions of this, but I would consider that evidence of early civilization in India rather than evidence of Buddha living c. 3000 BC.