Data formatting can be specified in the inspector to get the 12 July 1998 result once the data is entered. But the expected data entry order is controlled by the locality settings specified for your computer. (European locations expect dates to be entered in DDMMYYYY order while Americans expect MMDDYYYY order...)
You may need to also check the text tab in FIle Options to make sure that your file is using your computers settings.
"If i want to get 12 July 1998, the validation requires me to type 7/12/1998 which is(month/ day/ year)."
If you are not in USA and you are using a file created with a USA system, simply make a clone of that file and you'll have the correct date.
Thanks to you all guy. I managed to solve this problem by changing the date format of my Mac in system preference.
Now i can type 12/7/1998 to get 12 July 1998. Thanks!!!