Is there a specific way the virus affects people? What is the youngest age someone could conceivably Evolve? If I wanted to make someone who Evolved when they were ten, and had just turned 18 now, would that be possible? Would she have already been rounded up by Tac6?
Well... It makes them Evolve...
No, aside from making some individuals, for reasons unknown, Evolve, it doesn't affect people in any noticeable way. Those evolutions though can have physical affects (WardenIce's character for instance, sprouted wings).
In terms of the world, there is no limit on how young a person can evolve. Evolutions have been seen in infants. For players the absolute youngest someone could have Evolved is 8, which would make them 16 currently - because it's the youngest available age playable on E. Someone evolving at 10 and being 18 is absolutely fine.
Now as far as being rounded up by Tac 6... Unless you have something specific in mind - shoot me a PM about your idea if so - the characters in play are not currently being detained by Tac 6, they're all free. One of the potential starting scenarios may have them having been recently captured and escaping, but that'll be determined a bit later.