My brother and I recently received an inheritance after our mom died. He's never been very good with money, so I was proud of him when he used his portion to pay off his debts. But then he went out and financed a van that I know he still can't afford. I'm afraid he's falling right back into the same old money problems, but I don't know how to talk to him about it.
I've learned, after years of writing books, doing a radio show and trying to educate folks about their finances, you can't make people listen to you. Even with what I do for a living I don't throw my opinion around unless someone asks.
I think you're smart for realizing there are some boundaries here. But there's no reason you can't create a situation where he can ask your opinion. You might begin with talking about some of the mistakes you've made in the past. This could help him connect with you, and feel more comfortable opening up about his own situation. Once he realizes you haven't repeated the same mistakes, and have a better life for it, he might just ask how you did it. Then, the door is open!
But you can't become preachy every time someone does something dumb. That will only hurt their feelings and cause them to tune you out completely.