A little crazing and cracking is normal, particularly riding in hot conditions. Generally it is acceptable on the tread blocks and round the edges of the upper surface, but not if it's round the bottom.

Just out of interest, what's the date moulding on them say? They may very well be a lot older than 2 years.

Cracks like some of yours around the bottom of the blocks along the centre line are often caused by either extended hot running or pressures being too high. Low pressures and hot running tend to damage the outer most tread blocks. It looks like you've had a reasonable innings out of them, probably time for replacement? They are only going likely to get worse and eventually look like this, especially if ridden hot:

__________________