Anger being dismissed as childish

How do you deal with this, if you even can?

I've gotten into a habit of acting out when I'm angry/frustrated because I live in a household where my opinion has never mattered, and I have a younger brother who has basically had power over me for 7 years to the point I no longer even speak if he's in the same room.

Of course, the ideal situation would be to get out but that's not happening any time soon as I have no job.

I feel the urge to act out even more. Threaten to hurt someone (without ever actually doing it) because my words don't seem to get through to anyone.