Think it's impossible? Think again.
When we think of the past, we erroneously think of 10, 20, 30 years ago. We think of the distant past. What about the immediate past? As you are reading this post, your reading the sentence before this one happened in your past. And the moment you decided to read this post you changed your immediate past. From that moment forward, till your finished reading, every second back (immediate past) was spent on the words in this post.
What I am saying is that we change our past right now, in the present. I don't want to use the word "decide" because it gives the impression of affecting something at a later time. I don't want to say you decide your past by the actions you take now. It's right but not as right as using the word "change". Decide makes it look like the actions you take now, over time, constructs your future. But change makes it obvious that I mean the effect is instantaneous. Immediate.
The moment you take an action, right there, in that instant, it changes your past. Maybe, like me, you've never taken a beer before. The instant you open a beer, pour its content in a glass cup and take a sip, your past changes. Now you've taken a beer before.
Your past starts right now and as far back as you can remember. Why focus on the distant past when you can change the immediate past?
Take the actions you want to be part of your past and instantly they become part of your past. Maybe you want to be bilingual. Start now. You've always wished you had followed your entrepreneurial passion. Start now. For years you've wanted to visit a particular country. Go now (if you have the money, though). Whatever, you want to look back and tick as done, do now. And that's how you change your past.