Old wives tail about tires, true or not?

[mercman from oz]

I fitted these 17" Firestone Tyres that were made in New Zealand back in 1979. Last year, I drove 500 miles sitting at 55 MPH. They still look like new, and don't show any signs of cracks etc. The only problems that I have had is with the Tubes, as they start leaking around the Valve. I have had to replace 3 Tubes. As for cleaning, I use a kitchen cleaner with a small Nail Brush.