The type of failure depicted is called tread separation. Numerous examples can be seen on our roads, especially coming off from 18-wheelers. In fact this specimen is also from a commercial vehicle (tyres for passenger cars don't have such boring tread patterns).
Ever noticed what happens to a rubber band when you leave it for some time? The same happens to tyres. Although the rubber of rubber band and tyre undergo much different treatment, the base material is same i.e rubber.
The rubber of a tyre keeps losing its useful properties even when stored in a cold, dry (or otherwise ideal) place like a shipping go-down.
Once the rubber goes hard, it will:
Lose colouration. New tyres look really black [two definitions of new: 1) freshly manufactured, 2)unused]. Expiry tyres will look greyish. This is due to 2 reasons: 1) The chemicals which give tyre its colour are degrading just like the chemicals which are responsible for its structural integrity. [Tyre rubber is white by default, carbon black or other dye is added to make it look black]. 2) Sand/grit/other dirt will accumulate inside the surface cracks and make the colour look dirty (or anything other than the cherry blossom shiny black you expect a healthy tyre to look like).
Develop micro-cracking: Inspect the side wall closely and you will see micro-cracking. On a used tyre, these are fatigue cracks. On an unused tyre micro-cracking is seldom present (no matter how old) but if you install an expired tyre you will soon develop cracks in a few days.
Lose grippiness: Rubber in essence is in the same family of chemicals as bitumen (both are organic compounds). So it tends to stick to the asphalt. But once any of the two gets older, the attraction lessens (pardon the pun) and you start to witness longer stopping distances and increased steering effort to maintain intended course.
Lose structural integrity: Tyre is essentially multiple layers of rubber sandwiched with multiple layers of other material. Once the rubber gets older and hard, it is safe to assume that other chemicals have also lost their effectiveness and would result in a failure sooner or later. In Pakistan the traffic is slow therefore sidewall shredding or bead separation type of failure is less common but tread separation (as shown in quoted photo above) is more common.
Lose ride-comfort: Since the rubber has become hard, the tyre will completely lose its bounce and conformity and ride quality will become akin to a horse-cart with wooden wheels. This is an exactly non-scientific and highly subjective method of checking whether he tyres have become hard or not.
Increase road noise: That beautiful design that determines your tyreprint is called the tread pattern. It serves a practical purpose which is to reduce road noise through destructive interference of sound waves. Each tread block goes through a lot of sway and harmonic motion each revolution of the tyre. Once the rubber becomes hard, this squirm stops happening or (reduces in effect) and thus the destructive interference does not happen as efficiently as envisaged by the tyre R&D engineer, resulting in increased white noise &/or chirping.
By far the better method is to look for micro-cracking in the sidewall and/or tread.
Tyre pressure is always corrected when the tyres are cold (after running the car 2-3 km to the nearest shop, the tyres are still cold). So you should just maintain the required pressure and no adjustment is needed for prevailing weather conditions. Colder the weather, colder is the cold tyre temprature. Hotter the weather, hotter is the cold tyre temperature. When the weather is cold, tyre will take in more air to maintain required pressure. When the weather is hot, necessary pressure will be established with lesser air (or maybe you find that you have to bleed excess pressure).