Coolant operating temperature is around 90 to 95C. It's under pressure so the boiling point is higher than 100C
The radiator fan should kick in around that temperature a little below 100C
Debris in the cooling system will block the radiator and heater matrix 1st, not necessarily entirely, just enough to make it ineffective. You can get chemicals to flush the cooling system and this is cheaper than replacing anything.
Lots of things can cause overheating, lean running, head gasket problems, air locks and some others. it's difficult to diagnose remotely.