Using ;minage, you can require that all new members' accounts be created a certain amount of time ago. For example, if you minimum age of 3 months and a user that created their account 3 days ago tries to join, they will be kicked and sent a DM informing them of the account age requirement. Setting it to 0 disables it. For more info on this command, see the commands page on the main site.
See the custom commands page.