Sitting 190 lightyears from our solar system, HD 140283 was found almost a hundred years ago, and has been studied by astronomers ever since. Scientists knew the star was old due to it's composition of primarily helium and hydrogen, but it wasn't until now that they were able to narrow down its age and come up with any sort of number. It turns out that is roughtly 13.9 billion years, actually older than the universe—but there's a 700-million-year margin of error, which gives it plenty of room on the right side of the universe's birth.
Astronomers knew of another star that was almost this old, but the reading on this star in particular is far more likely to be accurate. It almost definitely is the oldest star we've ever seen. More here.