Function Aging

TZullo01 

VBA requires straight quotes instead of curly quotes.

Also, you're missing a few groups.

Try this version:

Function Aging(dos As Date, agedate As Date) As String
    'Calculates aging date based on date of service and an input age date
    Select Case agedate - dos
        Case Is < 0
            Aging = "DOS is after age Date!"
        Case Is <= 30
            Aging = "0-30"
        Case Is <= 60
            Aging = "31-60"
        Case Is <= 90
            Aging = "61-90"
        Case Is <= 120
            Aging = "91-120"
        Case Is <= 150
            Aging = "121-150"
        Case Is <= 180
            Aging = "151-180"
        Case Is <= 210
            Aging = "181-210"
        Case Is <= 240
            Aging = "211-240"
        Case Is <= 270
            Aging = "241-270"
        Case Is <= 300
            Aging = "271-300"
        Case Is <= 330
            Aging = "301-330"
        Case Is <= 365
            Aging = "331-365"
        Case Else
            Aging = ">365"
    End Select
End Function

Let's say AgeDate is in C1 and the dates in B3 and down.

Enter the following formula in C3;

=Aging(B3,$C$1)

and fill down.