I think the current USAian system of telling maturity by age is awful and not very functional; same logic as above. Setting criteria for citizenship and reassessing the population periodically might be a better idea. Assuming that anyone whose body is within these boundaries is a citizen is another approach. I don't have any decisions to pronounce; I'm still investigating issues.
Speaking of which, is scooterbird or someone going to summarize all this? I'm not sure which points are currently being discussed, or what the latest state of the discussion is, or how I'd tell. It'd seem that some form of DB would be useful, but I'm not sure how big a job we're talking about.