Honestly when ever you think you are ready. For some it's younger than others. For example My friends have been dating from 7th grade till now in 10th grade then there is me. I'm 16 and can't handle the drama that can come along with a relationship.
I started dating at 12, but whenever you feel ready and responsible, than that is when you start dating, if your parents have rules about no dating until you are a certain age, than I would wait because it is difficult trying to hide something like that... but whenever you are ready is the best choice.