Writing about the past

This may sound melancholic, but I've decided to write about the past today. How many times do we think about what we could've done in our lives if we had another chance? How many times do we think in how different it would be? Sometimes, all we want is to step back in times and remake our decisions, or even relive a good moment again.
The truth is we made mistakes and thats why we want a second chance, but we know some things don't have another opportunity. In my opinion, I should've lived my youth more intensely, also I should've studied more.
The good news is that I'm still young (I'm 25) and there a lot of things I still can do, so I don't have to look back my past and regret. Those moments are already gone. It was good while it lasted but new things are coming.

Writing about the past

This may sound melancholic but I've decided to write about the past today. How many times we think about what we could've done in our lives if we had [not wrong] given another chance? How many times we think in how different it would be? Sometimes, all we want is step back into the past times and remake our decisions, or even spend a good moment again.

The truth is we make mistakes [we still do :( ]  and that's this is why we want a second chance. but we know some things However, not often do we don't accept get another opportunity. In my opinion, I should've lived taken my youth more seriously intensely, also I should've and studied harder more.

The good news is that I'm still young (I'm 25) at twenty-five and there a lot of many things I still can do. So I don't have to look back to my past and regret. Those moments are already gone. It was good while it lasted but new things are coming.

Good essay.  Your English is good but needed more tweaking when writing formal essays.