Okay, strictly speaking Voyager 1 left the Earth 34 years ago, however the spacecraft is about to make another milestone--it is about to become the first object crafted by humans to leave the Sun's influence.
The solar system does not just encompass the planets, it is actually the entirety of the Sun's influence both gravitational and (in a limited sense) electromagnetic*. Voyager 1, at ~11 billion miles from the Sun is already out further than any other object made by humans. It is past the outermost planets, it is out beyond the
Kuiper belt and is close to what is known as the heliopause which is where the 'boundary' of interstellar space is considered to be. When it crosses that boundary, it will no longer be in the solar system and will truly be out in interstellar space.
http://www.popsci.com/science/articl...-new-data-says
Cheers
Aj