How to lock a column until it's last row with data - excel

Question

I have date mentioned in cell A1, ex - "May".
I am now trying to lock rows 2-last with column Z which mentions date of joining of each employee and compares it to A1.
If month of this cell Z is > A1 then I am trying to lock the row. Not sure what to do.
Below code doesnt help :
Sub Lockrow()
Dim DestSh As Worksheet
Dim lastrow As Long
Dim i As Integer
Set DestSh = Sheets("Consultant & Teacher")
With DestSh
'finds the last row with data on A column
lastrow = Range("A65536").End(xlUp).Row
'parse all rows
For i = 6 To lastrow
'if your conditions are met
If Month(.Cells(i, 26)) > Month(.Cells(1, 2)) Then
.Range("A" & i).EntireRow.Cells.Locked = True 'lock the row
End If
Next i
End With
End Sub

Answer 1

Is this what you are trying?
Sub Sample()
Dim DestSh As Worksheet
Dim lastrow As Long
'~~> Change this as applicable
Set DestSh = Sheets("Sheet1")
With DestSh
If Application.WorksheetFunction.CountA(.Cells) <> 0 Then
lastrow = .Columns("A:C").Find(What:="*", _
After:=.Range("A1"), _
Lookat:=xlPart, _
LookIn:=xlFormulas, _
SearchOrder:=xlByRows, _
SearchDirection:=xlPrevious, _
MatchCase:=False).Row
Else
MsgBox "Insufficient rows"
Exit Sub
End If
.Unprotect "MyPassword"
.Cells.Locked = False
.Range("A6:C" & lastrow).Locked = True
.Protect "MyPassword"
End With
End Sub