Er...I've been studying Japanese on and off for like 10 years and there's still stuff I can't play. Mind you I haven't exactly been doing it full-time, but there's a lot to learn.
That said, I've really only been using my Japanese skills to play import games for the last couple of years, and I think I have improved a lot in that time. Games can be really good practice tools. Look for games that have both text and voice and let you advance through the dialogue at your own pace. (i.e., visual novel-ish games, rather than modern, more cinematic cut scenes) Heck, some visual novels have a history function that even let's you replay the audio for past lines, though that's rare in any other genre.
But still, you're going to need some sort of foundation of basic skills before you should even think about playing import games. Looking up words you don't know is one thing, but you should at least know basic grammar and sentence structure. Learning kanji is a seemingly endless process, but if you don't even know hiragana and katakana then you should probably forget it.