Example sheet
Code
Sub Example()
Dim wks As Worksheet
Set wks = ThisWorkbook.Worksheets("Sheet1")
Dim units As Range
Set units = ThisWorkbook.Names("Units").RefersToRange
Worksheets("Sheet1").Range("Year_Max").Value = WorksheetFunction.Max(units)
Worksheets("Sheet1").Range("Year_Min").Value = WorksheetFunction.Min(units)
End Sub
Result