ChatGPT has enough guardrails now that it often refuses productive prompts. It's actually very very hard to get it to do what this person did, arguably impossible to do unintentionally.
As it stands, the human beings called OpenAI willingly did business with this child, and willingly generated the speech that persuaded him to kill himself and sent it to him. That they used a computer to do so is irrelevant.
They may have chosen not to age restrict it because
1) It's really not practical to do that effectively
2) more importantly (and they seem to care about this more than most companies) it would push kids to less safe models like those used on character.ai
What OpenAI does now is what trying to make AI safe looks like. Most of the people arguing for "accountability" are de facto arguing for a wild west situation.