Not bones but even better. Scientists found soft tissue from dinosaurs that was 75 million years old.

Can't speak for bone, but the bases of trees in a forest which is drowned due to sea level rise can remain as wood for many thousands of years. I suspect that in waterlogged but not anaerobic conditions the same would be true of bone.

On a similar note, bog bodies up to 10000 years old have been found preserved ("mummified") without fossilisation.

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Some Dinosaurs have been found partially unfossilized, one even in a fully non-fossilized state, with even the skin pigment preserved (mummification). It all depends on the circumstances surrounding it's burial over time. Of course, such finds are exceedingly rare.

You may find this of interest: https://en.wikipedia.org/wiki/List_of_dinosaur_specimens_with_preserved_soft_tissue

Those are still fossils that have mineralized, it's just material that usually doesn't survive long enough for that.

That claim has met with a lot of controversy, and even accepting it, these are like microscopic fragments of heavily degraded material.

Interesting. At the time I don’t remember them being described as microscopic. But it was many years ago.

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Fossilization is strictly the process where minerals have replaced tissue and bone, so as long as mineralization doesn’t happen you could have a bone as old as you want. It’s just hard to find them in nature because bone and tissue decays unlike minerals unless something like amber is involved.

I was wondering if the situation which would naturally preserve bones would end up causing fossilisation so if there is a limit in nature. Hadn’t thought of the amber angle, So potentially the tail of the dinosaur that was preserved in amber might still be bone?

Things that aren't yet fossilized are usually referred to as "subfossils" , which is probably how you want to search for this information

Anyway, I did some research and here's some things I found

This paper describes camel bones from about 3 million years ago on Ellesmere Island. They are embedded in layers of leaf and moss that are described as "subfossil" and the bones themselves were fresh enough to allow the removal of significant collagen for analysis. There have been reports of even older collagen/soft tissue, but that's in bones that have clearly been fossilized. I'm guessing these bones are closer to what you are talking about, given the context of their preservation.

Here's a similar study from the same area looking at beaver teeth and local vegetation, comparing isotope ratios to see what beavers were eating. So we are talking about plant and animal remains that still have organic material that isn't too heavily modified.

Finally, here's a paper that managed to snag DNA from mammoth teeth slightly more than a million years old. That's less than the previous studies, but DNA is more fragile than collagen, so we are talking better preserved specimens here.

Anyway, the answer is probably "A few million years, and you find them in frozen sediments"

Although who knows what might be frozen under the ice at the bottom of Antarctica