The conversion of a varchar data type to a datetime data type resulted in an out-of-range value.

hey, you shouldn't put a textbox.text inside your database query. That will open a huge cue to sql injection

cmd = new SqlCommand("INSERT INTO Login(Admin,Password,Age,Gender,Dateofbirth)VALUES('" + textBox1.Text + "','" + textBox2.Text + "','"+textBox3.Text+"','"+ Gender +"','"+this.dateTimePicker1.Value.ToString("dd/mm/yyyy hh:mm") +"')", con);

use add parameters instead. just like that link Peter provided you

cmd.CommandText = "INSERT INTO person (birthdate) VALUES(@date)";
            cmd.Parameters.Add(new SqlParameter("@date", dateTimePicker.Value.Date));
            //con is sql connection
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();

private void button1_Click(object sender, EventArgs e)
{
//do all  stuffs for creating command class's object
con.Open(); //con is the object of connection class

cmd.CommandText = "INSERT INTO person (birthdate) VALUES(@date)";
            cmd.Parameters.Add(new SqlParameter("@date", dateTimePicker.Value.Date));
cmd.ExecuteNonQuery();
con.Close();
MessageBox.Show("data Registered successfully!");
}

change datetime format like "dd-MM-yyyy" to "MM-dd-yyyy" now u get o/p