Tire pressure and tire longevity

[RedZ4]

I've been curious to know what people are running with their tire pressure here. Do we keep it to recommended specifications? What is the recommended specs for an E30 with 15" wheels?And as for tire longevity. I was told that if the tires are more than 5 years it deteriorates with the Malaysian heat. And it hardens so it doesn't provide good grip anymore. Any real truth in this? My front tires are about 5 years old. And they still have some thread in them. So what do I do? change them since I love to late apex a corner and drive at high speeds. Please advise. Thanks.