Should tyre sidewalls appear cracked so quickly? I fitted a brand-new pair of Schwalbe Marathon Racer tyres at the start of this year. I've just noticed that there are quite a lot of very small cracks in the side wall of both tyres. (The tread is still good though). Even using a worst-case estimate, I've only done about 3200km this year. Schwalbe say the Marathon Racers should last at least 5000 km? 

The cracks are very small, somewhere between Fig.1 and Fig.2 on the website. The bike has been stored indoors when not in use. They have been great tyres but I'm wary of spending that much on tyres if they need replacing every 8 months.



The cracks look like this in various patches most of the way round both sides of each tyre.

Addition:
Took the tyre and inner tube off to inspect. I can't see anything like the 'ripples/waves' in the Schwalbe pictures. Most of the slits are in the same position as those pictured above, i.e. between the start of the tread and the dynamo track. (A few are slightly lower though).
This doesn't seem like a terrible issue. You should be able to ride on these tires for awhile longer. I've seen people with super cracked tires ride for multiple months without issue. 

Oftentimes, cracks like this happen because of over inflation and exposure to the elements. To keep the tires viable for as long as possible, I would recommend keeping the bike inside when you're not using it, and leaving the pressure between 60 and 80 psi.