Dual nationals and permanent residents
Singapore does not recognise dual nationality beyond the age of 21. If you are male and a citizen of Singapore or you hold Singapore Permanent Resident (SPR) status you are liable for national service from the age of 16 up to 50.
From the age of 13, a Singaporean male is required to apply for an exit permit whenever he travels out of Singapore.
Male children granted Permanent Resident status as part of their parents’ SPR application are also liable for national service.
For further information see the following websites:
Immigration and Checkpoints Authority
Ministry of Defence (MINDEF)