I would first go to annualcreditreport.com and get all three credit reports and get the scores. Even though they may be FAKO, except for Equfax, it will still give you a general Idea of where he stands.
just to be sure that all reports are the same, since not everyone reports to all three credit reporting agencies.
Is the Cap One charge off in the process of being resolved? If not I would have him start to get that taken care of. Either settle for less or getting into a payment plan. If it hasn't gone to a CA yet then it would be wise to get it resolved before it does, because if it does, and it will, it will be a double whammy on his credit report. One for the OC and one for the CA, not good.
I'm assuming he has a bank account. If not he should set up a checking and savings account. Potential lenders love savings account so if he doesn't have one set one up.
After he has done all that then I would go back and look for a credit builder card. There are alot out there, but you two have to be very diligent on your search, since many have insane fees, from processing fees, to high annual fee's to application fees, so shop around. Orchard Bank and BoA seem to get the highest praise for credit building cards on this forum.
If all three Credit reports are reporting the same, it looks like he has one goodie and one badie, once the badie get's resovled he will be in better shape, not just credit wise but for his own financial reasons. He is young so he will be ok.