The bit of code in red is the problem
Dim iRow As Long
Dim ws As Worksheet
Set ws = Worksheets("Sheet1")

'find first empty row in database
iRow = ws.Cells.Find(What:="*", SearchOrder:=xlRows, SearchDirection:=xlPrevious, LookIn:=xlValues).Row + 1

'check for a Name number
If Trim(Metextbox_name.Value) = "" Then
Me.textbox_name.SetFocus
MsgBox "Please complete the form"
Exit Sub
End If

'copy the data to the database
ws.Cells(iRow, 1).Value = Me.textbox_name.Value
ws.Cells(iRow, 2).Value = Me.textbox_surname.Value
ws.Cells(iRow, 3).Value = Me.textbox_age.Value
ws.Cells(iRow, 4).Value = Me.textbox_gender.Value

MsgBox "Data added", vbOKOnly + vbInformation, "Data Added"
'clear the data
Me.textbox_name.Value = ""
Me.textbox_surname.Value = ""
Me.textbox_age.Value = ""
Me.textbox_gender.Value = ""
Me.textbox_name.SetFocus
End Sub