Creating a date column with date format in SQL

I'm creating a table that contains a date registered column. I want it formatted as "YYYY-MM-DD". I've already attempted this...

CREATE TABLE patient(
    dateregistered text format 'YYYY-MM-DD' not null
);

Now, the problem I'm having is, when I enter a date in a different format (i.e. 11-05-2015), it accepts that date in the table. Shouldn't it be giving me an error message or reformating it to the format I set? (I prefer the later, unless the data entered erroneous i.e. 32-13-20015)

Can someone let me know what I'm doing wrong?

Kind regards.