Conscription is referred to in art. 143 of the 1988 Federal Constitution which states that military service is compulsory.  
Conscription is regulated by the Military Service Decree. 
According to the Military Service Decree all 19-year-old citizens are liable for military service. 
But in practice it seems that men are called up at the age of 18.  
Military service lasts for 12 months, and may be extended to 18 months.