That's something that your parents should do.
How can I convince my 21 year old brother to get a job? He still lives at home but refuses to help out
You can't living free is super fun :)
Yeah that's not gonna happen....free....rent.....free....rent....free wins out every time! Until your parents find their proverbial kahonas he's stayin' put!
All the convincing in the world won't make much of a difference. If he has been enabled and encouraged to be a free loader .. He will continue to be a free loader.
I'm sure he knows full well what a typcial effort would be expected of him in terms of gaining self respect and showing some level of independency and even some ambition.
You can try to encourage him .. On a positive level .. It may not help but it can't hurt.