It is mandatory for all men. However, the system is getting much more lax than it was 20 years ago. The room for medical waivers is getting larger and with the US military realigning back to CONUS stations the need for KATUSA soldiers has also decreased. My best buddy in the Army was KATUSA so I know how the system works.
no it's only for men
it's a mandatory conscription for all korean men (and women i think) to do 2 years minimum service. usually it when they leave high school and before uni.