Google-sheets – Format cell if today is 2 weeks after date in another cell

If I understand you correctly, this can be achieved with conditional formatting in New Google Sheets:

The above with Format > Conditional formatting..., Custom formula is

=countif($H$1:$H$5,A1)  

Background checked and yellow chosen, with Range: A1:F6.

Apply to range A1:B conditional formatting based on custom formula

=$A1=MAX($A$1:$A)

The formula =X=Y returns 1 (true) is X=Y, and 0 (False) otherwise. So, formatting is applied (to both A and B) if the value in A column is equal to the maximal value in A column, as you wanted.

The dollar signs (absolute references) are needed so that as the formatting propagates throughout both columns, the references are still made to column A.

If there is a header row, adjust accordingly, applying

=$A2=MAX($A$2:$A)

to the range A2:B.

You can make this work on a single column or more than two columns: just change the range of formatting. The formatting formula should be written as it is to be applied to the upper left corner of the range.