You can be prompted for guarantor details when you try to save the registration details for a borrower below a certain age. To specify the age limit for the prompt:

1. From the Module Menu select Maintenance, Circulation and then General Parameters.
2. Enter a number in the Age limit for the guarantor prompt in borrower registration.
3. Press Tab or click anywhere on the screen to enable the Save options.
4. Click Save or Save & Close.

If the borrower is below the age limit then you'll see a prompt like the one below. You can click Yes to go to the Guarantor tab.