It's a difficult problem, for sure. I don't know that there CAN be an objective standard, because people are too individual. Some parents are very frank with their children or they actually find decent information on the internet, and they would be equipped for making informed decisions much earlier, while others get very little information except what they glean from their peers, much of which is bad information.

Laws, however, have to be pretty black and white in order to be effectively enforced. That's assuming one believes there should be a government enforcing laws in the first place. A lot of people here are anarcho-capitalists. I can't see that ending well, just letting the market decide on this issue.