Source: https://www.cmpb.gov.sg/before-ns/voluntary-early-enlistment-scheme/
All male Singaporeans and Permanent Residents will be enlisted for full-time National Service (NS) at the earliest opportunity upon turning 18. If you are at least 16.5 years old and wish to be enlisted before turning 18, you may do so under the Voluntary Early Enlistment Scheme (VEES). However, you will have to obtain your parent(s)' or guardian(s)’ consent and be medically and physically fit. You may have to go through an interview to ascertain whether you will be able to cope with military training.
The VEES application process is as follows:
Each VEES application will be decided on a case-by-case basis.
If you are no longer studying, or have just completed your GCE ‘O’ or ‘N’ Level but have no intention of furthering your studies, you will receive a Further Reporting Order with details to report for registration and medical screening. If we determine that you are suitable to be enlisted before the age of 18 years, you will be enlisted within four to six months after being given a definitive Physical Employment Status, subject to training capacity.
If you have graduated from ‘A’ Level or diploma studies overseas or are from a foreign school, you may have completed NS registration and medical screening earlier. You will be enlisted within four to six months after your course completion.