My husband is a juvenile probation officer and has dealt with many kids that huffed gas and paint. First, make sure he is huffing and talk to him. Most kids will deny it but you can look for signs such as old rags lying around and of course the cans are a major sign. The kids that he has dealt with have had to go to a rehab facility to get help because it becomes an addiction just like street drugs. Good luck.
You could try to talk to him quietly and ask about the cans you have found, he needs some help I think for sure, if he is on something it would affect him and his behavior.When he comes in do you act normally or do you get upset quickly , maybe some quiet time to talk if you can,Has he got a Dad around sounds like a Mans touch may help would his Dad be able to find out whats happening? Good Luck, not easy is it.