In my opinion (and only mine) it is when you are confident and competent in a variety of environments. For example, you did a deep dive with your AOW class. Are you now confident based on that one experience to go to 100ft with a buddy and not a DM or instructor? Why? Do you know how to gas plan for that depth? Do you know if you narc? What about your buddy, is he/she more or less experienced than you? In other words, if something goes wrong, do you know what to do?
Sometimes it will depend on where you dive. Can you dive in both cold and warm water environments? Some very knowledgeable and proficient warm water divers have issues when then need 7 mils of neoprene and 25# of lead. Many have never seen kelp or 5 ft viz. So in their usual environment, they may be able to handle everything the see, but change locations and they need to be a bit more cautious of their dive plan.
Experience and additional training (formal or with a mentor/buddy) is the key. The real answer lies with you. It could take 30 more dives, or 300 more dives. But at some point you will know. I still learn on every dive.