This bit sticks out to me:
I've just written to him saying that staying in our house comes with conditions - one of which is letting me know every day what he has applied for
That IS treating him like a child. He isnt, he is an adult. He shouldnt have to report back to you on a daily basis like this really.
He doesnt sound that bad a bloke, and is in the same situation as many his age at the moment. There is not a lot of work about, and there are lots of applicants going for every job. Even temp work, especially at this time of year is inundated with student who want to work during their summer breaks, or overseas students coming here for work too. His age group and limited experience will severely impact the jobs available to him, as there will be a lot more his age, but with a better CV.
Lots of lads his age make a fuck up at some point, due to drinking too much, and it rarely means they have an alcohol problem, and lots also dabble with recreational drugs, but dont go on to become totally dependant on it too.
If he is being a considerate "tenant" and looking after the house, then that is something. I know of plenty who would abuse that freedom, and it sounds like he does respect your home.
Help him with his job hunt, but dont be too controlling over it, or he will get arsey, you will get frustrated, and it will end up in a battle that will not help the situation.
There is always light at the end of the tunnel, and he will find something, but everyone is struggling right now. :)