Was suddenly pondering who decides that the legal age for adult hood is 21. Why 21?

Then what's the difference between 18 years old and 21 years old, besides the fact that mathematically they are 1,095.75 days apart?

In Singapore, you can legally gamble by placing bets with Singapore Pools or get your insides intoxicated with drinking alcohol and smoking at the age of 18 but you cannot watch R-rated movies till you reach 21.

What's interesting is at the age of 18, Singapore males can take up arms and be licensed to kill in the event of war but cannot enter into legally binding contracts, (except maybe for internet subscriptions and mobile phone contracts) or vote during General Elections.

And if someone breaks the law at the age of 18, then will he be sent to a home or straight to jail?

Maybe 18 is an age where the guys go through a manhood ritual called NS to transfer boys into men by the time they ORD at age 21, just nice lor, although some of those I know who went thru the ritual or worse, permanently stuck in the ritual in the form of regulars still act childish. Hmm, is it cuz they never ORD and 'pass' the ritual? Hahah. Anyways..

And for gals leh? They will be protected under by the law so that any guy who had sex (doesn't matter if the gal consented or not) will be charged with statutory rape so that means they are considered grown up the moment they hit 17 since they are no longer protected? Other than that, they follow the 18/21 rule same as the guys.

Weird rite?