There is no age for starting entrepreneurship. You can start whenever you feel ready. In fact, your youth will give you more energy, and "ignorance" to get started since you may not know everything, but you'll still keep going. More importantly if you start young, you have an advantage compared to those who start late, because even if your venture failed (which it might), you still have more chances to give it a shot since you'd still be young! So my advice would be to just begin!