(I don't want to directly answer the question because currently an answer will be mainly based on opinions. Instead, I will attempt to provide some information that, in the future, could allow us to more accurately predict when an AGI will be created).
An artificial general intelligence (AGI) is usually defined as an artificial intelligence (AI) with general intelligence (GI), rather than an AI that is able to solve only a very limited set of tasks. Humans have general intelligence because we can solve a lot of different tasks, without needing to be pre-programmed again. Arguably, there are many other GIs on earth. For example, all mammals should also be considered general intelligences, given that they can solve many tasks, which are often very difficult for a computer (such as vision, object manipulation, interaction, etc.).
Certain GIs perform certain tasks better than others. For example, a leopard can climb trees a lot more skillfully than humans. Or a human can solve abstract problems more easily than any other mammal. In any case, there are certain related properties that a system needs to have to be considered a general intelligence.
- Continual learning
Consider a lion cub that has never crossed a river. By looking at her mother lioness, the cub attempts to imitate her mother and can also cross the river. For example, watch this video Lion Family Tries to Cross River | Birth of a Pride. One could argue that all lions possess this skill at birth, encoded in their DNA, which can then fully develop later. However, this isn't the point. The point is that, to some extent, they possess the properties mentioned above.
One could argue that certain current AIs already possess some of these properties to some extent. For example, there are continual learning systems (even though they aren't really good yet). However, do these systems really possess autonomy? There should be a precise definition of autonomy (and all other properties) that is measurable, so that we can compare computers with other GIs. I am not aware of any precise definition of these properties. In fact, the field of AGI is really at its early stages and there aren't many people working on it as a whole, but people work more on specific problems or attempt to achieve certain properties (for example, there are people that attempt to develop continual learning systems, without really caring whether they show any autonomy or not).
There are certain intelligence tests that could be used to detect general intelligence. The most famous is the Turing test (TT). Some people claim that the TT only tests the conversation abilities of the subjects. How can they really be wrong, given that there are many other tasks or skills that are not tested in a TT?
Therefore, there are several questions that need to be answered in order to formally detect an AGI.
- Which properties does an AGI necessarily and sufficiently need to possess?
- How can we precisely define the necessary and sufficient properties, so that they are measurable and, therefore, we can compare AGIs with other GIs?
- How can we measure these properties and the performance of an AGI in applying them to solve tasks?
A paper that goes in this direction is Universal Intelligence: A Definition of Machine Intelligence. However, there doesn't seem to be a lot of people interested in these topics. Currently, people are mainly interested in developing narrow (or weak) AIs, i.e. AIs that solve only a specific problem, which seems to be an easier problem than developing a whole AGI, given that most people are interested in results that are profitable and have utility (aka cash rules everything around me).
So, there's the need for formal definitions of general intelligence and intelligence testing to make some scientific progress. However, once an AGI is created, everyone will likely recognize it as a general intelligence without requiring any formal intelligence test. (People are usually good at recognizing familiar traits). The final question is, will an AGI ever be created? If you are interested in opinions about this and related questions, have a look at the paper Future Progress in Artificial Intelligence: A Survey of Expert Opinion (2014) by Vincent C. Müller and Nick Bostrom.