Well, if we consider the decay rate of urban and rural areas and look at the materials used back in the golden age, as well as context given via lore. The golden age was a couple thousand years ago at minimum, then the dark age for several centuries, and now the city age. The iron lords disapeared roughly 400 years ago, and we know saladin would have been arround before that so at the verry least he would be around 400 years old(assuming he got res'd and immediatly joined the iron lords). BUT, in the trailer showing said battle roughly 400 years ago he still looks like an old grump, so either he looks that way cause guardians dont age, or we do age just very slowly, in which case hesbold as dirt.

It's hard to determine. No one really knows when the Collapse happened, but we do know that shortly after the Traveler made the Ghosts to revive humans of great potential. He's definitely centuries old, no doubt about it.

Individuals who were raised by the ghosts before the city existed were known as the Risen, Lord Saladin and the other Iron Lords/Iron Wolves were Risen who decided to follow the knights code of chivalry and protect the innocent. Seeing as how it took several centuries for the city to be constructed and the walls perfected, its very plausible Lord Saladin is somewhere around 400-500 years old. Take note thay Guardians are immortal beings and cannot die unless their ghost is destroyed or abandons them(dredgen yor). Guardians require no food, sleep, or sustenance of any kind other than the traveler's light. By this logic Guardians cannot age, but some Guardians do tire of the fight and relinquish there ghosts so they become mortal again. (old titan mark) https://www.bungie.net/en/Forum/Post/212980061/0/0/1