I know that one of the basic science principles is the suggestion of similarity of laws of nature. I.e. if we see ancient human fossils, similar to modern human remnants, then we should expect they are of similar age.
Well, similar physiology. Modern humans, throughout recorded history, rarely broke the 100-years-old mark. Our evolutionary cousins rarely break half of that and in the wild reach old age at our "Middle Age" equivalent.
So, knowing that as we are is exceptionally long-lived for members of our clade, it would be absolutely incredible and far beyond expectations for an evolutionary ancestor to live 8x-9x longer than some of the longest-lived members of our tree (and would be one of the longest living complex organisms ever).
Impossible? No. We can only interpret data from the past; we do not have any records from the time period. In that way, you're entirely correct if you're looking for additional proof.
But does science have some other age proofs besides this?
This depends on what you consider 'other' proof. Most of the estimations of age of found fossils relies on comparative morphology: We assume that because our joints and teeth wear-out at a certain rate, we can compare the rate of decay of teeth and joints of fossils and get an estimate. If it's true that our extinct cousins experienced similar wear 'n tear as we do (and we don't have any reason to think otherwise; the bones may be slightly different, but they are made up of the same material), then we can use the comparative morphology as a reasonable estimate.
If we assume that their bones and teeth wore out much, much slower (it would have to be about 10x slower while also being made of similar material) then our age estimates would have to be adjusted.
May be, for example, from migration data or from some other sources?
Migration data would be incredibly difficult to produce. You would have to follow one family as they migrated, and fossils are rare enough as-is. Data like that would be practically impossible to gather.
Perhaps some Population Geneticist has run some genomic data and is capable of making a similar claim through the molecular clock hypothesis, but I am as-yet unaware of anything like this.
Isn't it possible in principle, that some virus epidemic in ancient times cause humans to live shorter, due to virus DNA embedded into all of the human DNAs?
In principle? Yes. But there isn't any evidence for that. Keep in mind that in order for the viral DNA to be integrated into all of humanity then it would have had to infect us when our numbers were very, very small. Evidence does show a bottlenecking event in humans about 70,000 years ago - but this was thought to have been caused by a supervolcano eruption which dramatically changed the environment and not a virus. Both genomic and geological evidence come together to support that hypothesis.
So, while you are correct that - in theory a population of humans could have been infected by a virus which mutated their DNA and caused a dramatic reduction in lifespan at the same time as a bottlenecking event - we have no other evidence supporting that, either genomic, geological, or evolutionary.
Given the lack of evidence, we should remember our Occam's Razor - In the absence of evidence, the simplest explanation is usually the correct one.
So it's either an exceptionally long-lived species of an already-long-living family contracted a virus at the same time a bottlenecking event occurred and didn't leave behind any evidence, or our ancestors lived about as long as our evolutionary cousins do now and it's us who are exceptionally long-lived because of evolutionarily advantageous things like The Grandmother Hypothesis and advancements in technology - which is supported by genomic evidence, fossil evidence, geological evidence, and recorded history.
We cannot ever truly know what happened several hundred thousand years ago. We weren't there and nobody was writing anything down. However, Science is evidence-based, implying that scientific opinion follows the argument with the most supporting evidence behind it.
If the evidence changes and begins to favor another argument, then so will the scientific community (ideally speaking).