SOLUTION ONE
$this->db->where('id','3');// here we select every column of the table
$q = $this->db->get('my_users_table');
$data = $q->result_array();
echo($data[0]['age']);
SOLUTION TWO
// here we select just the age column
$this->db->select('age');
$this->db->where('id','3');
$q = $this->db->get('my_users_table');
$data = $q->result_array();
echo($data[0]['age']);
SOLUTION THREE
$this->db->select('age');
$this->db->where('id','3');
$q = $this->db->get('my_users_table');// if id is unique, we want to return just one row
$data = array_shift($q->result_array());
echo($data['age']);
SOLUTION FOUR (NO ACTIVE RECORD)
$q = $this->db->query('SELECT age FROM my_users_table WHERE id = ?',array(3));
$data = array_shift($q->result_array());
echo($data['age']);
