Legally or unofficially? Because some people are ready before the legal age of consent and many who are over it are still not ready. Turning 16, or 18 or whatever the law is in your area does not magically make you ready. What makes you ready is a certain level of maturity, awareness and self-confidence. In other words are you sensible enough to take all the health and safety precautions into account? if not then your not ready. Are you ready to deal with the emotional impacts that sex often has on your life? If not then your not ready. Are you prepaired to potentially deal with the consequences of your actions (such as becoming a parent, or chosing to abort)? If not then your not ready. Sadly it is difficult to tell if your ready, because sex is not really like anything else so you never really know the true nature of it until you have it!
However, that I think it is a question that can only be answered by a lot of introspection, self reflection and critical thinking, all of which takes maturity and honesty to do. Just be honest, if you feel your not ready, there is no shame in that, do not feel pressured into having sex before your ready! It has to be your decision. Do not make the decision lightly! For many feel they are ready, but really, they are not! Consider that!
But if you have really, really thought about it and come to the conclusion that your ready, and that this is truly what you want...go for it!