Only a parent can be the judge of their childs maturity level. I have seen teens who are oblivious to their surroundings, and I have also seen 9 and 10 year olds who are surprisingly astute.

My son is now a military policeman and daughter is a pre-med student. They are both very aware of their surroundings. We started early and discussed these issues with them eg: What would you do if a stranger said "Your mother is in trouble and she asked me to bring you there". Or what would you do if a stranger tried to touch you? Are there some places you should not go alone? etc. You don't have to go into the grisly tales of the abductions, as 'they might try to take you' will probably be sufficient motivation.

We still discuss current events and situations with the college age daughter, but the son carries a rifle and a pistol, an asp and mace with him at work and faces different kinds of danger. The daughter is not paranoid, but very aware and always keeps her car door locked and the tank full, and has a cell phone, mace (in hand), and a whistle with her when walking the campus.