We can assume that Xavier lived a regular human lifespan. Same with Magneto, cloning aside. Sinister, he might have stuck around, but probably not for that long. So why oh why did it take Apocalypse two entire millennia to rise to power? That's one thing I'll never understand. The other is Cable. Who is this mysterious failed father from the future who also has a twin that sometimes inhabits his body? Your guess is as good as mine.
"I have intermerged my substance with Nathan's, my friends..."
