According to Korea's Military Service law, He can postpone his military service until the age of 37.
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Article 149 (Management of Emigrants, etc.)
(1) In cases where any person liable for military service who has continuously resided abroad or his parents fall under any of the following subparagraphs before he reaches 25 years of age, he shall be deemed to have obtained permission for overseas travel up to 37 years of age: <Amended by Presidential Decree No. 22286, Jul. 21, 2010; Decree No. 23305, Nov. 23, 2011>
1. Where the principal or his parents obtain permanent resident status (excluding conditional permanent resident status) in a foreign country, or he or they obtain indefinite stay status or long-term stay status of not less than five years in a country that does not enforce a permanent resident status system and continuously reside abroad;
2. Where the principal or his parents obtain stay status as special permanent resident or permanent resident in Japan and continuously reside abroad;
3. Where the principal continuously resides together with his parents in a foreign country after he was born in such foreign country and has obtained the foreign country's nationality or citizenship;
4. Where the principal or his parents emigrate to any foreign country in accordance with the Emigration Act and continuously reside abroad; 5. Where the principal departs from the Republic of Korea with his parent who are not a resident employee before his age of 18 and continuously reside