You could use a custom 'user defined function'
Open the VBA window by right-clicking the worksheet name tab and 'View Code'
Then right-click the highlighted worksheet name in the left-side pane.
Select 'Insert' then 'Module' (not Class module)
Paste this into the large VBA window on the right-side:
Public Function Plus14(datecell As Range)
If IsDate(datecell.Value) Then
'is a date so add 14
Plus14 = datecell.Value + 14
'not a date, so return blank
Plus14 = ""
Click File - Save from the VBA menu bar
This is pretty basic - no error checks etc.
Click Alt+f11 to return to the main Excel window.
If you have dates / other values in column A, starting at A1, put this in cell B1:
Drag the formula down from B1 as many rows as you have data in column A
This function will return a value which is the date + 14 days if the referenced cell contains a valid Excel date. If the cell does not contain a date it returns "".
You will need to format the cells with the date format required.
I don't think that you can format the cell with the user defined function automatically from within the function - but perhaps someone else will say if it is possible.