You are entitled to withdraw from your KiwiSaver account when you reach the qualification age for New Zealand Superannuation (currently 65) or five years after joining KiwiSaver, whichever is the later if you joined before 1 July 2019. If you joined on or after 1 July 2019 you will be eligible to withdraw when you turn 65.
If you are going to buy your first home, you may be eligible to withdraw some of your KiwiSaver savings to put towards it. If you have owned a home before you may still be eligible to withdraw your savings in some circumstances.
In limited circumstances, you may be able to access some of the money in your KiwiSaver account earlier.