Cracks on the side of fairly new tire Today I noticed that the sides of my rear tire has these cracks

The tires have been installed last June, and since then have always been used at the proper pressure (initially at the low end of suggested range, in the last 3 months in the upper end). The bike is stored in a shed or, when I go to work, in an underground garage.
Is it normal to have these cracks? I have always seen them on rather old tires.
They may have been stored improperly (e.g. near a heater/source of ozone) or been old when you bought them. Also, if you wash your bike, you might be washing away some of the protectants in the tire from the manufacturer. That being said, this wear does happen relatively quickly depending on the conditions. 

In any case, tire cracks are not a big deal -- they don't affect the structural quality of a bicycle tire significantly. Replace the tire when you get punctures (which will likely happen before the cracks in the sidewalls and stuff become a problem) or you have structural damage (e.g. bulges in the sidewall). You can use armor all or something to help prevent cracks though.