You can “tell someone what to do” but if it’s force that you use to get them to do what you tell them to do, you’ve already lost. Children should only do what parents tell them to do if they respect the advice of their parents. They will only respect the advice if it is usually good advice. Hypocritical advice is not good advice, unless you tell the whole truth behind the hypocrisy—admitting mistakes and showing efforts to change.
Respect has to do with consistency and honesty and wisdom on the part of the person who wants to be respected. You don’t have to be good in order to be honest or have wisdom.
Respect for the adviser isn’t the only part of the equation. There’s another aspect to advice and how it is received: how the advice is given. You can tell someone what they should do, or you can tell them how you learned or earned the wisdom you are about to impart. The second usually works better. If the person you are talking to can see the whole story, warts and all, it has more credibility.
I believe the saying: “information wants to be free.” The more we know, the better off we all are. In other words, innocence is not a good thing. I believe your sibling will be better off if you share your experience with him.
Share your experience! Notice I do not urge you to tell him what to do. I think you should tell him your story. What you did; why you think it is a mistake; how you care about him; how you hope he will make different choices than you did.
In doing this, you have to be aware that he did not ask you for any advice. I don’t know what your relationship with your brother is. I don’t know how close you are, nor how much you have shared with him in the past. I don’t know how well you trust each other. So figuring out how to share your story with him is up to you. You’ll have to pick a time and place where you can be private, and that is conducive to sharing secrets.
Tell him your story. Don’t tell him what to do. Tell him what you wish you had done. Tell him which decisions you regret. Tell him what your hopes for him are. But don’t tell him what to do! After that, it’s up to him.
Doing it this way allows him to make his own choices, but with the benefit of knowing your experience and your thoughts about your experience. He doesn’t have to figure out everything on his own, unless he wants to. In telling your story, I would tell it honestly—both the good and the bad. I wish I knew what you were talking about—what kind of mistakes you are talking about. But, my advice is generic, I guess. Good luck.