I have a problem with filter data between 2 textbox

private void Button1_Click(object sender, EventArgs e)
        {
            SqlCommand selectCommand = new SqlCommand();

            var filterConditions = new[] {
        CreateSqlFilter("Name_Arabic", txtName_Arabic, selectCommand, false),
        CreateSqlFilter("gender", CBgender, selectCommand, false),
        CreateSqlFilter("CIVILIDD", txtCIVILIDD, selectCommand, true),
        CreateSqlFilter("status", comboBox1, selectCommand, false),
        CreateSqlFilter("username", txtusername, selectCommand, false),
        CreateSqlFilter("City", comboBoxCity, selectCommand, false),
        CreateSqlFilter("Governorate", comboBoxGovernorate, selectCommand, false),
        CreateSqlFilter("confirmation", comboBox2, selectCommand, false),
        CreateSqlFilter("NATIONALITY", CBNATIONALITY, selectCommand, false)
        // etc.
    };

            string filterCondition = filterConditions.Any(a => a != null) ? filterConditions.Where(a => a != null).Aggregate((filter1, filter2) => String.Format("{0} AND {1}", filter1, filter2)) : (string)null;

            using (var connection = new SqlConnection(ConfigurationManager.ConnectionStrings["my"].ConnectionString))
            {
                selectCommand.Connection = connection;
                selectCommand.CommandText = filterCondition == null ? "SELECT * FROM tabl2" : "SELECT * FROM tabl2 WHERE " + filterCondition;
                connection.Open();
                SqlDataAdapter adapter = new SqlDataAdapter(selectCommand);
                DataTable dataSource = new DataTable();
                adapter.Fill(dataSource);
                dataGridView1.DataSource = dataSource;
            }
        }

        private string CreateSqlFilter(string fieldName, Control userInputControl, SqlCommand command, bool exactMatch)
        {
            string searchValue = null;
            if (userInputControl is TextBox) searchValue = ((TextBox)userInputControl).Text;
            if (userInputControl is ComboBox) searchValue = ((ComboBox)userInputControl).Text;
            if (String.IsNullOrWhiteSpace(searchValue)) return null;

            if (exactMatch)
            {
                command.Parameters.Add(new SqlParameter("@" + fieldName, searchValue));
                return fieldName + " = @" + fieldName;
            }
            else
            {
                command.Parameters.Add(new SqlParameter("@" + fieldName, "%" + searchValue + "%"));
                return fieldName + " LIKE @" + fieldName;
            }
        }

SqlConnection con = new SqlConnection("Data Source=DESKTOP-J7D5POF;Initial Catalog=ilswork;Persist Security Info=True;User ID=****;Password=*****;connect timeout=900");
           SqlDataAdapter sdf = new SqlDataAdapter("select * from tabl2 where age between'" + txt1.text + "'and'" + txt2.text + "'", con);
           DataTable sd = new DataTable();
           sdf.Fill(sd);
           dataGridView1.DataSource = sd;