I started [doing X] when I was [Y years old].
Since then, I've...
If I had to do it all over again, here are 5 things I'd do differently.
Thing #1: Don't do X.
At the time, I thought [this] was a good idea.
It wasn't.
It led to [problem 1], [problem 2], [problem 3].
Instead, I would do Y.
Thing #2: Do X instead of Y.
I really thought X was going to give me [the result].
It didn't.
Instead, I would do Y. Because I learned much later that Y...
Thing #3: Do X, first.