[Jacob]

I've never read the comics, but from what i understand there's an Alternative Dimension storyline called 'The Age of Apocalypse'. Obviously, they can miss that part out. ...as well as the whole thing of him being part Alien technology, part Mutant.

But Apocalypse is basically the oldest Mutant there is, born in Egypt.

"Apocalypse's story begins with his birth in mid-30th century BC ancient Egypt during the First Dynasty. He was born disfigured in the settlement of Akkaba and abandoned in the desert to die. He was the last child born in the settlement before the nomad raiders, the Sandstormers, slaughtered the area's population. Their leader, Baal, found the child and considered it to have the potential to be a god. He raised the child as his own.

He named the child En Sabah Nur ("The First One"- see below) in anticipation of others like him. The tribe lived and died by the philosophy of survival of the fittest (with "fittest" being defined as toughest, most ruthless and pitiless). En Sabah Nur earned the right to adulthood at seventeen by surviving an endurance test in the desert. He and Baal were the only Sandstormers to survive when General Ozymandias attacked their camp. They found refuge in nearby caves, but Baal was killed when the cave he was in collapsed. En Sabah Nur, however, escaped to the surface, only to be enslaved."

...it then goes off into Time Travelling shenanijinks and the like, but the film could have it so that Apocalypse was buried by the Egyptians who enslaved him, fearing his disfigurement.

Yadda-yadda-yadda, Centuries later he emerges all "Roar" and the like.