You have to convert the literal to DATE with the help of TO_DATE since DOB is DATE data type.
TO_DATE('', '<format_model>')
For example,
SQL> CREATE TABLE t(dob DATE);
Table created.
SQL> INSERT INTO table(dob) VALUES(TO_DATE('01/10/2018', 'DD/MM/YYYY'));
1 row created.
SQL> COMMIT;
Commit is complete.
SQL> SELECT * FROM table;
DOB
----------
01/10/2018
A DATE data type contains both date and time elements. If you're not concerned about the time portion, then you'll also use the ANSI Date literal which uses a hard and fast format 'YYYY-MM-DD' and is NLS independent.
For example,
SQL> INSERT INTO t(dob) VALUES(DATE '2015-12-17');
1 row created.