As I was growing up, inevitably, I met people who left a negative impression on me. As I think of them today, I have the tendency to think of them as the same person I knew then with exactly the same qualities. Then I think of the person I was then. I think of what my life was like before God regenerated this wicked heart and made me a new person. Even as a Christian, I know the person I am today is different than the person I was 5 years ago.
When the opportunity arises now to meet people from the past, I try to take into account that they have had many life experiences since I last knew them and have likely matured in ways that I cannot imagine. I try to extend to them forgiveness and grace, as it has been extended to me.
And then I start asking questions to find out about the person they are now. And I listen.
Young person, you would do well to store this information away for later use as you will surely not escape the need for it in the future. (Listen to the woman in her 40's and you might not have to repeat her mistakes).