How time flies! It has been almost 5 years since I left the little island. Miss the tropical weather, and of course all the hawker centre food!

Anyway, I'm looking for an updated info on applying for exit permit in current situation. My son will be turning 13 in few months time.
I rang CMPB when he was 12 to ask about the procedure. The staff told me to ring them again when he turns 13, they will provide a temporary password for him to apply for exit permit.
I then asked how does the bond work? We are now residing in Aust permanently, and also have taken up Aust citizenship. I am single parent (ex-Singapore PR) with full custody of my son. My son will renounce his SG citizenship once he has completed the NS. The staff told me that if he just apply for 2 yrs exit permit, he won't be needing a bond. Then he will just have to renew it every 2 year until he reaches the time to serve NS. Just wonder if anyone has been on the same path and renewing the exit permit every 2 yr? Any renewal applications had been denied?
Also, when should I apply for exit permit exactly? few months before he turns 13? so that by the time he turns 13, then he has the paperwork approved? But I remembered I read in other posts long time ago, someone advised to apply when the son is 13yr 1 month old. Although, I don't understand why.
Happy to connect with other parents who are in the same boat. My son was born in year 2008.