Whoa, apparently,
photons cannot touch each other?! So, they will never experience time.
I guess this is why:
From quantum electrodynamics it can be found that photons cannot couple directly to each other and a fermionic field according to the Landau-Yang theorem[11] since they carry no charge and no 2 fermion + 2 boson vertex exists due to requirements of renormalizability, but they can interact through higher-order processes or couple directly to each other in a vertex with an additional two W bosons: a photon can, within the bounds of the uncertainty principle, fluctuate into a virtual charged fermion–antifermion pair, to either of which the other photon can couple. This fermion pair can be leptons or quarks.
There are at least eight terms I don't know at all in that explanation!