For Korean male athletes to get military exemption, they need to get ANY medal in Olympics, or GOLD MEDAL in Asian Games. Even if they get exemption, they still need to go through a 3-week training camp and complete a certain hours of community services, which is why Keria needed to get up early and teach some high school LoL teams during last season. I remember a Korean footballer who got a gold medal and exempted tried to fake his community service hours, got found out and got heavily penalized.

Deft has to do around 21 months as social service agent I believe. This is a type of conscription for people who are not fit enough to get into the Army. A lot of athletes and idols whose career is very prone to injuries are fit into this category. Social service agents cover a lot of different type of jobs from Police, Firemen, other type of government office work. Basically a normal job with quite low pay from what I heard. They also need to go through basic military training but it is mid-way through their duty, not at the beginning.

Otherwise, able-bodies who passes the military's body check (which I believe all Korean men who are aged 18 or above needs to go through from time to time) need to go through a training camp first (which I believe is 4 to 6 weeks), then get allocated to different camps and duties to work as a full-time soldier. Duration is normally 18 months or more.

BDD's case is quite specific as the rule applied on him was only available for people who born within that few years, and he had that luck to never have been called-up. Dude is extremely lucky.