That would make the earth 6,017 years old today.
He was only off by about 4.5 billion years.
But here's an interesting thing: his reputation is being rehabbed somewhat by legitimate scientists these days. Not for his answers --- they were dead wrong --- but because he did the best he could with the currently-available data.
New data yields new results, and Ussher can't be held at fault for information that wasn't available to him (or anyone) in his time.
Science is always only a best, current approximation of the truth, with the certain caveat that new knowledge may require new answers. Scientific beliefs are mutable, based on increasing knowledge. Science self-corrects, over time.
In contrast, religion claims to have eternal truths that are unaffected by facts or new knowledge --- which leads to silliness like Creationism and Intelligent Design and Climate Change Denial, which require that you deliberately and consciously ignore whole bodies of demonstrable, objective facts. Religious dogma is immutable, contrary facts be damned (or ignored). Religion almost never self-corrects, believing that it got everything right the first time.
So, it's interesting to see modern science rehabilitating Archbishop Ussher's reputation. He was a religious guy, but he was trying to do science, and to base his conclusions on what were then the best-available facts.
And that's all any rationalist can do, isn't it?