"The news last week that exoplanet Gliese 581g may be in the "goldilocks zone" and could therefore hold liquid water and alien life got everyone all excited, with good reason. A potentially habitable planet--and only 20 light years away! But to put things in perspective, here are a couple of estimates on what it would take to travel to Gliese 581g. One scientist puts the travel time at 180,000 years based on current space flight technology, while another explains that it could be quite quick if we build a matter-antimatter drive, and can figure out how to bring along 530 times as much mass in fuel as is contained in the ship and cargo itself."
At the rate of technological advancement I reckon we will have the capabilities to reach this planet at the earliest of 2040-45