1. 1.6 mm

2. As long as no sidewall damage or cracks on the sidewall, by all means use it. Tyre lifespan is 10 years.

Yes wet braking is a function of tread depth as the void on the pattern helps you evacuate water.

The question is how bad your wet braking distance will be ?

You could see a quick comparison between the wet performances of a 1.6mm tread depth vs full tread depth tires

MICHELIN Primacy 4+ (new : 22,8m - worn : 31,5m) versus BRIDGESTONE TuranzaT005 (new : 22,6m - worn : 36,4m); CONTINENTAL PremiumContact 6 (new :23,1m - worn : 35,3m); GOODYEAR EfficientGrip Performance 2 (new : 23,8m - worn : 35,5m) competitors.

You loose about 10-14m or so. This is a huge difference especially when it comes to an emergency brake situation on wet.

Hence my advice is , please change your tires ! if not please be aware of the risk you are taking.

Everyone has their own theory so to speak. Some said waiting a couple months for the rubber to cure (like wine aging) while some swear enjoy the smooth and soft rubber compound for noise free ride. I think it is all bullshit for normal and daily driving.