Why is C increasing in the first years?

[mariopaolucci]

This is due somehow to the aging of population. If we change

to-report calculate-age
  report floor ((ticks - birth-tick) / ticks-per-year)
end

into

to-report calculate-age
  report floor ((1 - birth-tick) / ticks-per-year)
end

The phenomenon goes away. See the figures from a run without crimes and without births

with age:

without age:

Is this ok? My opinion is that this is due to a slight increase in the number of people at risk, that only afterwards reduces - that is, due to population structure. But playing with the such population structure didn't convince me completely.

[mariopaolucci]

In the end it is the age range - if I run with everybody the same age, I get c jumping right where there's a threshold in the file.