You can refer to the post above for a dev answer on ‘population and GDP link’ and related ideas. In short - population affecting GDP, tax revenues, and many others will mean a massive increase in complexity with few player choices. Nonetheless, I agree that it would be nice if there’s another way of fighting debts instead of just taxing more & spending less.
Regarding youth & retired demographics, you may be right but imo the youth isn’t getting much love from devs. At least the retired population will increase as lifespan & health go up though. But, to be fair, I won’t give attention to statistics that will have an impact 100 turn (=100 quarters = 25 years) later. There will be a massive amount of time and its effects should be creeping at unnoticeable speed.