You can retire whenever you want. The government decides when to start funding it.

As for why - the same reason why they get to decide what side of the road you drive on and what laws you follow. They rule the patch of land you were born on, and if you don't like it you can either participate in the system (assuming it's a democracy) or leave.

It doesn't (you can retire early), but it does decide part of what you will need to be saving and how.

And the reason it decides that, apart from "because it can", is because many societies have seen what happens when it's left to individuals to take care of this, and they fuck it up in massive numbers, and the outcome of that then fucks up society.

The government decides when we can retire and they help us out. You can stop working today if you want, Government shouldn't pay you for it for no reason. Your duty as a citizen is to work and build your nation, eventually the government pays back that service with benefits.

This question cannot be asked in good faith on a user board. It requires an 800 pages book on politics, history, philosophy, economics to be properly answerered and it would barely scratch the surface.

You might as well ask similar questions about most basic laws and concepts behind how western societies work.

The government doesn't decide when you retire. The government decides when it is willing to pay you to be retired.