For example, when we look at the sun, that’s 8-minutes-old light. When we look at Polaris (the North Star), that light is 447 years old.
When we look at Andromeda?
Yeah, that light is 2.5 million years old.
https://booksforkeeps.co.uk/article/visiting-uncle-albert/
The intuition you can develop about special and general relativity from these books is pretty amazing!
It's not an easy task from the prospective of a photon, which can be easyly proven with just two little slits.
Experiencing time and having mass are linked in a very deep way. Objects that experience time, i.e. have some kind of state evolution, must have mass, this is how we know the neutrino has mass even though it's smaller than we can measure, because we measure them oscillating between the various flavours of nutrinos.
This is also how the Higgs mechanism gives rise to "rest mass" in most particles, by constantly exchanging weak hypercharge with them. This oscillation back and forth gives them mass.
There's also a different thing that GP might be hinting at, which is that by convention we assume that the speed of light is the same in all directions, but there are other conventions we can use as long as the round-trip speed of light agrees with that which we've measured (and yes, we can only ever measure the round-trip speed of light, FYI). Another convention is that all the light we see takes zero time to get to us but the light we emit goes out at half the speed one would expect with the standard convention (known as the Einstein synchronization convention). So instead of "light we see from Alpha Centauri is 4 years old" or "we see Alpha Centauri as it was 4 years ago" we can say that we see it as it is right now, but this is not a very commonly used convention.
In a lab setting, yes, but across such distances, no. Photons don't have a cycle counter on them, so they don't keep a cycle count and can't reveal that cycle count. All we can do is measure frequency/wavelength (spectrum, really, since we're going to see lots of photons, not really onesie/twosies) and intensity, and we can use the astrophysical distance ladder to figure out roughly where the emitter must have been.
So a photon emitted in such a direction takes no time (from the photon's point of view) to be absorbed by its destination... only it has no destination and never will. It gives "what if a tree falls in a forest with no one to hear it?" vibes. Does the universe sort of "lose" the energy of that photon in a way that it doesn't for photons that are absorbed? Is it like The Great Memory Leak of the Universe or something? Is our existence leaking out between the fingers of the hand of God?
Therefore you can't measure the speed of light in any one direction. You can only measure the round-trip time of flight (e.g., if you have the detector at the emitter and use a mirror).