Firstly you have to be 21 years old or above.
Secondly the requirment for applicaiton of credit card is usually local/PR need s$30,000 per anuum income and foreigners s$60,000 per annum for Classical MasterCard/Visa, and s$45,000(local) s$60,000 for American Express/ Gold Mastercard/Visa.
Ether support by Income Tax of Assessment of CPF statement. Some accept computer-generated payment slips also
If you have enough income can apply.

Heard some banks will issue credit card to those who deposit certain amount in there bank, but never found one... :P

The most important thing: Debit Card is your own money while credit card is the bank's money.
There are much more limitaions of Debit cards.

另外用信用卡的人不一定开销就大哦， 我一个月才花一两百，少的时候甚至才不到一百。