is that supposed to be sarcasm?
I was pointing out the innate idiocy of assuming people would die of old age in a setting which even older people than her have been living for multiple centuries. The humans have been given machine bodies according to law, this drastically increases the human lifespan. Albert, Mikhail, Thomas and Ciel all appeared with the same age as when they were initially given the machine bodies, meaning they're older than Ciel and are originally citizens of Neo Arcadia. Ciel to this date still looks like her teen to twenty year old self.
As for the incident with Serpent:
X^X AD
Return of Mavericks -> Guardian Established by First Commander -> Guardian researching the Maverick cause in order to stop it.
->
X^X AD
-Serpent is caught in a Maverick attack, he survives and joins Guardian.
->
X^X AD
-Guardian Recon Unit uncovers a Fragment of Biometal Model W at Cinq Ville's Area F (The scrapyard). First Commander calls it BioMetal Model W. They research Model W.
->
X^X AD
-Guardian about to give up. Serpent, a member of the Recon Unit and the most passionate about the research, goes mad. He is empowered by Model W. The Recon Unit faces Serpent attempting to give the First Commander enough time to escape. However, the unit is mostly annihilated and all research data of Biometal Model W is erased by Serpent.
->
X^X AD
-Data of Serpent's betrayal is left behind by the remains of the Recon Unit that fought Serpent.
-The First Commander gives an order to protect the survivors of Maverick attacks.
-The First Commander managed to get away from Serpent, she vanishes into the Outlands. -> There the First Commander uncovers and seals away the Model W Core. Based on the data recovered from Model W, she creates the other Biometals and leaves passwords in each of the Biometals to unlock Model W's seal. -> Shortly after their creation, the Biometal's memories of recent events are erased. She attempts to hide the Biometals from Serpent.
From there, we know Serpent is unaware of the Model V Core and Ciel's biometals. With his Model W he uses his company Slither Inc. and his Model W to stage himself as the hero of Cinq Ville. According to employees, Serpent behaves normal until the appearance of a mysterious man and woman. From that time onward he had been digging around the outlands like a possessed man, looking for the Model W Core and the Biometals Ciel left behind.
It's thus Pandora and Prometheus who came to Serpent and sparked his interest in Ciel's legacy. Related to that is that they're well aware of Ciel as the commander of guardian and that she's centuries old, remarking that Prairie too is centuries old, based on her acquaintance with that woman.
Furthermore, tying into the erased memories of the biometals who had been hidden in the outlands for a very long time; Albert considers them a legitimate part of the game and even seemingly adapted it to suit their arrival. As such, he created the Model A, established ciphers that unseal only when there's battle with Ciel's biometals. Model A too is stored in the outlands and gets updated periodically with the situation on the chosen ones. His game of destiny that solely used Model Ws had turned into something completely else, yet he never once acknowledges Ciel's involvement. In many ways, everything she did to counter Model W was according to his plan. It's thus very possible that the missing memories of the Biometals relate to their knowledge of Albert.