I'm still percolating the idea that Herpo the Foul was never defeated, and endures as new identities every 50-100 years. Flamel was his attempt at creating a plausible identity that he wouldn't have to change for a while.

Edit: this is after his stint as Salazar Slytherin, mind you. After a while, being the bad guy just gets old...

 

There was a vampire in the Anita Blake books that turned out to be so old, he didn't even start out as a human before he was Turned: He was actually homo erectus, or the like.

It would be rather amusing if some pre-human shaman stumbled upon a method of pseudo-immortality, like horcruxes or the so-called Philosopher's Stone.

Everyone's wringing their hands over how this man and his wife have a Philosopher's Stone, and it must be so complex because only one person ever figured out how to create it...

In the meantime, the few who personally met Flamel knew that he was hairy as a bearskin rug and looked like he fell out of the ugly tree, hitting every branch with his face on the way down. He was just a bone rattling shaman who got lucky with his 'magic potions,' in between mastodon hunts.

"We're not banging rocks together here, we know how to put a man back together." - Cave Johnson