DATEDIFF with filter

This code does exactly what you need it to do.

Previous Date =
VAR PreviousRow =
    TOPN (
        1;
        FILTER (
            Blad1;
            Blad1[old date] < EARLIER ( Blad1[CRH_REQDATE] )
                && Blad1[job] = EARLIER ( Blad1[job] )
        );
        Blad1[old date]; DESC
    )
VAR PreviousValue =
    MINX ( PreviousRow; Blad1[old date] )
RETURN
    DATEDIFF ( PreviousValue; Blad1[old date]; DAY )

If this reply solved your issues be sure to mark it as the solution.