What is the correct age to start sex?

I can’t remember exactly what age I was when I had full sex. I don’t remember the date but I remember the settings. It was at a friend’s home, at a couch bed. I must have been 20 or 21 or 22. I had to go to work the next day and I thought whoever saw me next morning would immediately understand that I’d had sex the night before. Well, it didn’t happen that way. Nobody understood anything or would have cared even if they did. That looked like a big deal for me at that time but it wasn’t. Life went on as usual. Everything looked OK. I assume it must have been the correct age.
That was decades ago. Now, today, when I have children of my own, I’m trying to figure out what is the correct age to start having sex. I know it differs from culture to culture, from country to country, from person to person. The “proper age” is different in the United States than it is in Turkey. Or in Istanbul. Or even districts of Istanbul: Concepts are different in Bebek and in Sultanbeyli.
Considering that sex with a teenager is a crime in many societies, then this is a tough call. In some societies, far away from here, the president married his wife when she was 16. While he was 30-something. A young economist who you think would’ve known better. Well, the main opposition leader, again in a very distant country far away from here, who you would really think should know better, married his first cousin... Anyway, back to the age…
 I want to find the correct answer given that we are in Turkey, in Istanbul, in the year 2012. In a place right in between East and West where social values are so much intertwined, it is difficult to find the correct answer to anything… A modern, urban society ruled by a conservative government backed by the United States.
 What do you tell the kids? What do young people do? What do teenagers do? Do they know about birth control? When the prime minister wishes to raise a religionist generation, does that mean the age to start sex, or even thinking about it, is further postponed? He also advises women to have three children, which might or might not have an effect on the sex lives of Turkish women and men, but this is a completely different subject.
What do young people do, what do parents advise their young in this complicated society of ours? Is high school too early, or is it university? Or should they wait until they get married? Or is this sentence too archaic to even ask?
Do you have different recommendations depending on whether you are parenting a daughter or a son? What would I have done if I were 20 years old right now?