I would want to tell myself to stand up to my mother in my early twenties and not wait until I was nearly fifty to do so. Also, to have stuck by my sister when we were both young instead of being persuaded to see her through my mother's eyes.
My excuse then that as I couldn't get a student's grant my parents were paying for my further education, and I didn't think it right then to accept their money and then run counter to their wishes. And I still don't think that would have been right.
So if I had done as I pleased then, my life would certainly have been very different, as I wouldn't have the education I have.