Date in Excel

jenniferbrookplaza 

Pre-format the cells with Custom Format: 00\/00\/00
When entering the values always use ddmmyy, not ddmyy nor dmyy

(works no problem here - Excel 365)

EDIT: As pointed out by Hans & Sergei the above suggestion doesn't generate the actual date values you expect. As an example entering 010121 will display as 01/01/21, however if you reformat the cell with a Date format you'll see that the actual Date value is 09/16/1297

If you don't know how to convert to enterred values as actual dates, one way below. Assuming the enterred values start in A2, in B2 (or C2...) enter (and copy down as necessary):

=DATE("20"&RIGHT(A2,2), MID(TEXT(A2,"000000"),3,2), LEFT(TEXT(A2,"000000"),2))

(adjust the 20 to 19 if the dates enterred by your coworker are in 19xx)

Then select all cells in the column where you enterred the above formula > Copy > Paste special > Values. Finally delete column A