Reapply PR after 21

Check the eligibility criteria for an individual to apply PR. It’s clearly mentioned in ICA website. See below:

“As a foreigner, you may be eligible to apply for permanent residence if you are a/an: Spouse of a Singapore citizen (SC) or Singapore permanent resident (PR) Unmarried child aged below 21 born within the context of a legal marriage to, or have been legally adopted by, a SC or PR.”

Hi Surya2k, thanks for reply, what I mean is, is that any re-apply process needed to me after I'm 21 (was applied and get PR at 18yo). Last time my father applied for me when I'm 18yo

It has validity of 5yrs. So, after 5yrs it will be reissued and ICA will send the details of it. You can look out for the information and appointment (if required) near to its expiry.

Your PR will continue to be valid (you only need to apply for a new Re-Entry-Permit every 5 years, just like before). No new application needed.
You will, however, contuinue to be counted as second generation PR, which means you are liable to serve in the military!
If you give up this PR (e.g. to avoid national service), you will probably never get another one.