Earlier quoted context omitted.
The age of the attacker is irrelevant to Twitter's role in this story. However your underlying point still stands. If we want these types of attacks to stop, we can't just let all these companies off with a public embarrassment being the primary punishment. At a certain point we have to start calling it negligence when companies fall for these attacks and fail to have proper precautions in place to prevent them.
From memory, I recall the FBI did a study, and found that half of their employees would plug in a USB drive that they found on the ground in the parking lot. After training, that number was reduced to a quarter. If a security-focused government police agency is so vulnerable, it is unreasonable to expect perfection from a (less paranoid) company.
2. I think you may actually have it backwards. I would imagine the engineering group at Twitter (the people who have important credentials) is in some ways more paranoid, or at least more technically savvy and therefore more aware than many of the people at the FBI.