If you want to define an one-to-one relationship, you need define your entities like this:

• customer: { int id(PK), String name, int age, int passportId(FK) }
• passport: { int id(PK), String passportNumber, int customerId(FK) }

Each entity references each other with a foreign key to have that relationship, and the foreign key relationated with its IDs need to have same data type.

Try it...