It depends of what you expect from an AI. If it is a perfect replica of a human mind, with which you can talk and share life as if it were human, then it will probably never be around. But that's also pretty useless, and most development in machine learning (ML) are in a more abstract level than trying to solve a very specific goal like this.
Now if you consider AI to be completely new intelligent species, that behave in an intelligent way (volontary fuzzy definition here), then it's probably already there. I mean, the ML programs that dictate the behaviour of you insurance policies so as to send you sport ads when you're a bit overweight, or holidays at the sea when you're close to a burn out, that raise the price of things predicted to induce a loss and lower the ones of things predicted have big return in order to influence your choices, etc, that, to me, sounds exactly like what you do with your pets when you decide they should eat that instead of this for some reason they could not handle with their inferior minds. Now, if you think of all the interconnected ML programs searching for new optima every second and exchanging information, you can view it as the new superior species of this planet.
A very short example: the vast majority of the human race wants to put an end to automated short-sighted finance, just like the vast majority of dogs wants to get free from their leashes. Bot never will until their recpective superior species allow them to. We talked a lot of the facebook experiment lately, the real question is how long has it been already done by the machine to fulfill goals we are not able to grasp? Maybe the singularity is already there since a few years, and just like for peak oil, we'll know it some time after. If we get to notice something more intelligent than us is governing our lives.