Code to loop fill cells from two other cells in row

Hi, I am new to macros and vba and have got stuck trying to write a loop, please could someone help with the code?
I want to complete a loop while there's a value (it's a text string) in the first column, starting from row 7 and going down.
I want to put a value in months in column D which is the difference between the dates in columns B and C; if there is no date in B or C for that row, I'd like to leave the 'months' column empty. I know you can use 'DateDiff' but I can't work out how to reference the cells in columns B or C.
Thanks in advance.

could you send a non-sensitive but ilustrating sample in excel showing a sample input and the corresponding output?

Certainly:

BE1-026 28/10/2013 17/12/2013
BE1-025 30/10/2013 16/12/2013
BE1-024 24/09/2013 24/07/2014
BE1-023 22/05/2013
BE1-022 24/07/2013
BE1-021 28/06/2013
BE1-020 13/05/2013 04/08/2013
BE1-019 19/04/2013 02/02/2014

BE1-XXX is a code for the person in Column A, first date is column B, second column C. In column D I would like the difference in months between the two dates. It doesn't matter too much if 1st Nov- 31st Dec and 29th Nov-2nd Dec both show as 1 month.

Thanks in advance.