For singles to qualify for HDB resale, you need to be minimum 35 years old and holds singapore citizenship.
There is no minimum CPF required but for the amount that cannot be paid using loan, have to be paid in Cash if you do not have enough CPF.
Cash and cpf requirement is depending on how much bank loan you are eligible to. For HDB loan you should check out "HLE application" on HDB. HDB loan can cover up to 85% of the flat price.
An extra thing to take note which is not in your question, how much CPF usage you qualify to use is also based your age in comparison to the lease left on the HDB unit.
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