In South Korea, it is mandatory that all men between the ages of 18 and 35 enlist for training in the military. This law has been in place for decades and is unlikely to end soon. It is mostly in response to the ongoing war with North Korea, which is still technically active.
All men are required to take physical and mental tests. If they meet the requirements, they become active duty soldiers. Active Duty soldiers are separated into three categories – all with different lengths of service times. There are Marine Corps (21 months), Navy (23 months), and Air Force (24 months).
If the person does not meet the physical and mental tests, they have to do non-active duties such as a civil service worker, public service worker, or police officer.
Exemptions from military service are rare. The only way one can be exempt from their service is if they can prove that they are the sole available caregiver to someone else who cannot take care of themselves. Even if someone has an injury or disability, they are given light of alternative equivalents to military duties.
Again, it is unlikely that the mandatory conscription laws will be appealed or the service lengths shortened any time soon. Many Koreans think that it will only go away if they finally settle their war with North Korea which – in my opinion – is unfortunately unlikely to happen in the near future.
Most information can be found here: https://en.wikipedia.org/wiki/Conscription_in_South_Korea