I was going to flippantly say, "You'll begin to speak your mind freely once you get into your 60s, but then I read all the good advise and felt guilty.
For years, I tried not to create waves because I hate confrontation, but as I've gotten older, I've learned to stand up for myself and speak my mind. This is in real life, face to face with real living people, not on line. But I would also say that you have to choose your battles and decide what is significantly important and what isn't, because I let 99 percent of the things that confound me, pass. You also have to make a judgement, based on whether the person you're talking too is capable of understanding what you have to say. Many people aren't.
My wife is in poor health, and when the medical profession doesn't deal effectively with and for her, I become her advocate and in those situations, I will speak my mind. I'm almost always calm, collected and polite, but there are times one has to be confrontational when someone's well being hangs in the balance.
There have been a few times on the job that I have told someone off. It has always been in a situation where I was not being respected, and that's something I will stand up to. I do have a line in the sand. It is a very liberal line, and modestly drawn, but at the same time, if it is crossed, the person will know about it.
On this site, we are a support group so I always try to be kind and understanding. If someone offends me or simply annoys me, I don't respond, rather than provoke an argument, because those kind of arguments are almost always pointless and useless. By the next day, I've completely forgotten about it anyway, so it couldn't have been very important.