Like @ParaParaYukiko, I have not been long out of the ranks of the teenaged and I think it depends entirely on the parenting style. My mother was never one to tell me that I couldn’t do this, that or the other thing. What she would tell me is why she had done something not so great and let me decide whether or not I would do that. She wasn’t the kind to get drunk in high school or do drugs or get into fights but she was a terrible student. The only reason she graduated high school on time was because my grandfather was the president of the board of trustees at her school and so her teachers were told they couldn’t fail her. No, really. Once, a teacher failed her and he got yelled at and had to change her grade. She told me this was because she was the youngest and hated hearing, “Now, are you smart like sister A or hard-working like sister B?” and just said fuck all to the comparisons.
There were a lot of times in school that I resented my mother for being angry at a bad grade I got because I was always one of the best students in the school. I think I maintained my grades, despite her academic failure, because she never told me that I would be in big trouble if I failed. Her response if I did badly on a test was, “Why?” If, for example, she had seen me studying for hours, then she wouldn’t get very angry and would instead try to pin down why the test was so hard for me to do. If I just slacked off, well, then she got angry.
Basically, if you’re not hypocrite, then telling your kids the stupid stuff you did when you were younger shouldn’t be too big a problem. If, however, you’re the kind of parent who says, “You can’t smoke pot!” and then you tell your kids that you smoked in high school, they’re going to think, “Huh, well, it didn’t kill mom or fry her brain or do any of the stuff she says it will do so i bet it’s actually okay.”