I visited Japan 5 times for vacation when I was between the ages of 19 and 32. I would have gone more except it is not cheap. It is a great place to visit. The people are friendly, but a little shy. Most people do not speak English but they can read it OK. (Reading is stressed on the college enterance exams but there is no test on speaking). You can learn enough from a phrasebook or intro language book to get around.
Some tips:
Get the JR rail pass. It allows unlimited travel by rail and is available only to foreigners (it's THAT good a deal that they ban their own citizens from using it or else the rail system would lose money).
Stay at business hotels. They are MUCH cheaper than tourist hotels. The only downside is that, again, no one will speak English. The price differnce though is worth it (more than $150 difference a day). These aren't the capsule hotels that drunk Japanese stay at when they miss the last train home. I never stayed at those. These are just regular, if a bit smaller, hotel rooms.
Lastly, you can find some forums where Japanese post online and ask if anyone wants to hang out when you are over there. You will have many Japanese that want to meet forenginers and will be happy to show you around. And if you are single...