I have a sort macro. How to add script to preselect rows to sort based on column value?

I have a macro which performs a sort for me.

I have it set up to perform the sort on whatever rows are preselected by the user.

I would like to have the macro preselect the rows to sort for me, based on whether there is any value in a certain column (it will always be the same column, 'G'). All cells in column G presently contain either nothing, or a number between 1 and 20. I prefer the macro select rows based on whether there is any value in cells in column G at all, as I may add additional numbers later.

EDIT: Oh, and if it helps, all of the rows with a value in them will always be contiguous to one another. All of the blank cells are at the top and bottom (but those exact locations vary.)

This is what I'm using that I want to add on to.

Sub Sort()
'
' Sort Macro
' Sort based on column 'G'
'
' Keyboard Shortcut: Ctrl+m
'
    ActiveWorkbook.Worksheets(ActiveSheet.Name).Sort.SortFields.Clear
    ActiveWorkbook.Worksheets(ActiveSheet.Name).Sort.SortFields.Add Key:=Selection.Columns(7), SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:= _
        xlSortNormal
    ActiveWorkbook.Worksheets(ActiveSheet.Name).Sort.SortFields.Add Key:=Selection.Columns(4), SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:= _
        xlSortNormal
    ActiveWorkbook.Worksheets(ActiveSheet.Name).Sort.SortFields.Add Key:=Selection.Columns(3), SortOn:=xlSortOnValues, Order:=xlAscending, DataOption:= _
        xlSortNormal
    With ActiveWorkbook.Worksheets(ActiveSheet.Name).Sort
        .SetRange Selection
        .Header = xlGuess
        .MatchCase = False
        .Orientation = xlTopToBottom
        .SortMethod = xlPinYin
        .Apply
    End With
    Selection.Rows.AutoFit
End Sub

Thank you for your help. I'm a total rookie at this VBA stuff. But at my small firm, I'm the default "techie" by virtue of everyone else being even more clueless than I am. lol