I for one think that this is an interesting topic.

From what I see, this sort of thing shouldn't have a rule set in stone. Why? How rapidly one ages and how long one lives is completely independent of how someone else (even of the same species) does. Some people will age quickly, some will grow scars in battle, some will have their eyes gourged out, some will be burnt by magical fire, and there are even some more natural and less violent ways that show that someone is approaching their expiration date.
That being said, I would not think that a Xacha who claims he is 500 cycles is being fair. But, a very frail Xacha of 90 cycles I would buy.
My opinion? Take the suggested age limits into consideration, then push and pull at it in a sensible and fair manner.
For the actual aging, I would guess that the process is proportional to the life span. (Otherwise the 200 cycle demorian will be a black peanut.) But I wouldn't go as far as to say that there is a simple fraction to be used against all the inhabitants of Yliakum. Again, be reasonable, but this decision should be up to the RolePlayer.
And as for laws that govern different age groups (i.e. the one year of weapons training), I think that the most appropriate way to determine who is/isn't appropriate is to go not by age, but by character. For example, I know of an 11 cycle klyros who is quite intelligent and fairly skilled with weapons. (But then again, Klyros only live to 50, so that's actually old

, but anyways...) A government official should deem him ready for training because he is physically and mentally ready for it. But the 50 cycle Demorian who babbles to himself and wears a diaper would not be ready for such training.
Just my two-five cents.