⚠️SPOILERS⚠️
Let's start with the short part: Cooper. In the crossover with "Demons Within", Thistle talks about Cooper with Resnick. Later, Cooper pulls out what looks like a bible or religious book and starts talking about Mother Earth, but since it's Resnick's POV, he gets lost in his own thoughts and stops listening. By the way, you need to play the first chapter of "Demons Within" to get the code for chapter two.
Now, the dream scene between "Luke?" and "Max?" is weird, but there's this line that stands out:
"Well, it's been like a thousand freaking years and I've been dying for one of those herbal coffees."
He seems to at least remember his life before the world broke. And since Luke can loop through time, what feels like a couple of years for the dogs could be hundreds of years for him, kind of like what the Observer tells Gunner after Alon's vision:
"To you it felt like no time passed at all… but to me… FUCK!!"
So when Luke says "a thousand years", it's genuinely unclear whether that's an expression, literal, or just his skewed perception of time.
There's also Alon's theory that humans shatter when they overuse their powers. According to him, Luke has been unusually careful, and maybe that's exactly why he lost his memories: as a way to protect himself from breaking apart.
In Alon's route, when he describes his vision of a future Luke:
"You talked about yourself. About the nature of our realm. About the Humans, the Monsters and us. How everything came to be. At least as much as you knew yourself."
"You were there when everything started and, as fate would have it, you were there to see the end too."
Luke never explicitly says he's thousands of years old, but the context makes it pretty clear he's been around longer than anyone else.
One last thing, the Observer recognizes Luke immediately and says:
"You... I know you. You are Dawn's brother, aren't you?"
And we're definitely not talking about his lion brother Sansun.