On what basis please?
Not on the facts that you describe.
He can always appeal but then he has to show that his sentence was manifestly excessive. It might be but then he would have received advice to that effect from his barrister.
Also, he is out of time. He had 28 days from the date of sentence to appeal although generally appeals are not refused if they are good ones because of delay.
It is not a good idea to take advice from other inmates.
Can I clarify anything for you?