If you have a username attached to a publicly posted comment, people will be able to see your history. The internet is forever. Publicly posted comments are, by definition, not private. Treating them as such, in any capacity, is a mistake.
The biggest thing is to not post personal details, or to even post accumulations of details over many comments that can narrow things down. The weather where you are at the time, what type of car you drive (or your lack of a car), what type of job you have, etc, etc, etc. On their own, each of these pieces of information don’t mean much, but you start putting them together and you can narrow things down considerably.
It is also not a bad idea to occasionally throw in some misinformation about yourself. Maybe you don’t drive a Corolla, but instead a Hilux.