Thermostats can last a few years or decades all down to luck they are replaceable items that need replacing when faulty it's the closing return spring that goes soft over time .
2 ways of checking from a totally cold start feel the top hose to the radiator and the radiator itself ( avoid the fan just in case ) if it's warm before getting to operating temperature then thermostat is lazy not sealing properly replace or when engine is at standard operating temp for your vehicle mine is 84°C if you have a long downhill section on at 60-70 mph road put car in neutral and coast down the hill 1-2 miles long if you have it . If thermostat is good it will close off fully and you may lose 5°C when mine was faulty the temperature plummeted quickly going below 70°C within 30secs ( bearing in mind it was about -10°C❄ 🥶 when I tested mine )
When I checked the old thermostat with a feeler gauge it wouldn't even take a 1mm and only a scrap of daylight and torch light was going through yet that was the issue shows what such a small microscopic gap causes the new ones must clamp tightly shut )

 

always replace with OEM not cheap patten versions