Automating A Macro Range To Hide Rows

I have a graph in Excel containing the 12 months in column 'A' and data associated with each month in column 'B'. I want to hide rows containing months which have yet to arrive (eg: if we are in August, I want to hide the rows containing September:December). However, I want to change the range of rows that I hide each month (so that when we get to September, I only hide rows containing October:December). My attempts at writing a macro to perform this automatically have failed? This is the script I have written:

fyi - RowStart is the row number associated with January, RowEnd is the row number associated with December and RowNext updates each month and is the row number associated with the next calendar month.

Option Explicit
Dim RowStart As Integer
Dim RowEnd As Integer
Dim RowNext As Integer

Sub Hiderows()
RowStart = sheets("month").Range ("A1")
RowEnd= sheets("month").Range ("A2")
RowNext = sheets("month").Range ("A3")
Sheets("month").Select
Rows("RowStart:RowEnd").Select
Selection.EntireRow.Hidden=False
Rows("RowNext:RowEnd").Select
Selection.EntireRow.Hidden=True
End Sub