Earlier quoted context omitted.
....Because that's not possible today with current technology? edit: I seriously don't understand how you immediately jump to that being the new functionality when sending payments today is as simple as logging into paypal or any numerous other payments sites.... Not to mention the age requirement of 18? This comment is just fear mongering.
If you think the age requirement is even remotely effective, you're fooling yourself. I'm not suggesting that it will be frequently misused -- but even one mishap could seriously harm their business. Law enforcement takes child pornography more seriously than just about any other offense, and money on the table makes it even more serious.
If you are speaking about adults selling pictures of abused children back and forth, this'll be no different (even less secure) than current technologies that pedophiles use to avoid detection.