.NET/ASP/C# Web Site : Database Register Form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using Model;
using System.Text;

public partial class Register_Default : System.Web.UI.Page
{

    ModelContainer db;

    protected void respond(object output)
    {
        // Response output using StringBuilder
        var res = new StringBuilder();
        res.Append(output);
        ctrlRes.Text = res.ToString();
    }

    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        // Check all fields are not null
        if (firstName.Text != "" && lastName.Text != "" && howOld.Text != "" && emailAddress.Text != "")
        {
            try
            {
                // Attempt to int age
                int age = Int32.Parse(howOld.Text);
                // Check age limit
                if (age <= 17)
                {
                    // Under age - Error handler
                    respond("<div style='color: red; font-weight: bold;'> Sorry, you're not old enough to register... </div>");
                }
                else
                {
                    db = new ModelContainer();
                    // Query selector
                    var tbl = db.tbltst_table.Where(c => c.email == emailAddress.Text).FirstOrDefault();
                    // Check it is taken or not
                    if (tbl != null && !string.IsNullOrEmpty(tbl.name))
                    {
                        // Email exists - Error handler
                        respond("<div style='color: red; font-weight: bold;'> This email already exists, please <a href='/login/'> login</a> to continue... </div>");
                    }
                    else
                    {
                        // Insert the new record
                        tbltst_table nadd = db.tbltst_table.CreateObject();
                        nadd.name = firstName.Text;
                        nadd.email = emailAddress.Text;
                        nadd.surname = lastName.Text;
                        nadd.age = age;
                        db.tbltst_table.AddObject(nadd);
                        db.SaveChanges();
                        // Completed - Success handler
                        respond("<div style='color: green; font-weight: bold;'> Successfully registered, you can now <a href='/login/'> login</a>... </div>");
                    }
                }
            }
            catch (Exception)
            {
                // Age is not as an integer - Handle error
                respond("<div style='color: red; font-weight: bold;'> Please state your age numericaly ie: 18... </div>");
            }
        }
        else
        {
            // Missing required fields - Handle error
            respond("<div style='color: red; font-weight: bold;'> Please fill in the required fields... </div>");
        }
    }
}