Using If Statements to stop loading next form

Question

My age check isn't working so you can enter any age you want and it doesn't show an error and messageboxes don't show. It allows you to enter any information and still continue regardless. Any ideas?

Dim errorcount as Integer = 0

Private Sub btnContinue_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnContinue.Click
    strName = txtName.Text
    strAddress = rtfAddress.Text
    strCity = txtCity.Text
    strEmail = txtEmail.Text
    strHomePhone = mtxtHomePhone.Text
    strMobilePhone = mtxtMobilePhone.Text
    If txtName.Text = "" Then
        MessageBox.Show("You must enter full name", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    ElseIf IsNumeric(txtName.Text) Then
        MessageBox.Show("Please enter a valid name", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    End If
    If txtAge.Text = "" Then
        MessageBox.Show("You must enter your age", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    End If
    'Declaring age check
    Dim AgeCheck As Boolean = False
    If IsNumeric(txtAge.Text) = True Then
        AgeCheck = True
        'strAge = Integer.Parse(txtAge.Text)
    ElseIf strAge < 18 Then
        MessageBox.Show("You must be over 18 years old", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
    ElseIf strAge > 125 Then
        MessageBox.Show("Don't be stupid. You're not that old.", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
    ElseIf AgeCheck = False Then
        MessageBox.Show("You must enter a valid age", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        Exit Sub
    End If
    If Not IsNumeric(txtAge.Text) Then
        MessageBox.Show("Please enter a vadid age", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
    End If
    If IsNumeric(rtfAddress.Text) Or rtfAddress.Text = "" Then
        MessageBox.Show("Please enter your address", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    End If
    If IsNumeric(txtCity.Text) Or txtCity.Text = "" Then
        MessageBox.Show("Please enter your town/city", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    End If
    'if no index hasd been selected
    If cmbCounty.SelectedItem = "" Then
        MessageBox.Show("Please select a county", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    End If
    If Not mtxtHomePhone.MaskCompleted Then
        MessageBox.Show("Please enter a valid home phone number", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    End If
    If Not mtxtMobilePhone.MaskCompleted Then
        MessageBox.Show("Please enter a valid mobile phone number", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    End If
    If txtEmail.Text = "" Then
        MessageBox.Show("You must enter a valid email address", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
    ElseIf Not txtEmail.Text.Contains("@") Then
        MessageBox.Show("Not a valid email address", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        errorcount += 1
        Exit Sub
    End If
    If errorcount >= 5 Then
        MessageBox.Show("Too many errors. Shutting down", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Warning)
        Me.Dispose()
        Exit Sub
        'End
        'Exit Sub
    End If
    Me.Hide()
    frmCreditCardInfo.Show()
End Sub
End Class

Answer 1

your if statement - If IsNumeric(txtAge.Text) = True Then

If that equates to true, none of the elseif statements will fire, you're merely setting AgeCheck = True and that's all. You will need to rework the logic a bit

Answer 2

1. You need to handle when IsNumeric(txtAge.Text) is false.
2. You need to exit sub, when error is encountered

Try this block

If IsNumeric(txtAge.Text) = True Then
    strAge = Integer.Parse(txtAge.Text)
    If strAge < 18 Then
        MessageBox.Show("You must be over 18 years old", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        Exit Sub
    ElseIf strAge > 125 Then
        MessageBox.Show("Don't be stupid. You're not that old.", "Error", MessageBoxButtons.OK, _
                        MessageBoxIcon.Error)
        Exit Sub
    End If
Else
    MessageBox.Show("You must enter a valid age", "Error", MessageBoxButtons.OK, _
                    MessageBoxIcon.Error)
    Exit Sub
End If