[@Natty]

Basically, he's been 11 years old for the past 80 years.

The in-universe explanation for this is that the Nega-Bands connect him to an alternate dimension where the passage of time is disconnected with that of the main universe, essentially disassociating Billy from normal space-time. If you look in the Character Notes, you'll see mention of this in the second bullet under that heading.

It's a bit of a reference to [url=https://www.roleplayerguild.com/posts/4511079]another Absolute RP[/url] where I wrote Billy as Captain Mar-Vell. Billy suffered a subdural hematoma as a result of an intergalactic conflict crashing down on Fawcett City, and the Nega-Bands prevent that hematoma from progressing. So, its a means of extending his death rather than saving his life.

As his story matures, it's possible that Billy will be healed of the condition that required Aelfyre to use the Nega-Bands to save his life. But, starting out I wanted to write a young Billy Batson and then see where the story would venture off from there.