Learning languages is very fun but you're not going to learn Japanese on your own. You might learn some phrases and words but the language is just too far removed from English to learn without intensive classwork and immersion.
For a language like German or Swedish which is practically English with an accent this is much more doable, but once you start moving out of the Germanic or Romance (and especially Indo-European) trees language learning gets exponentially more difficult.
Coming to school I thought I'd take Russian for fun since German came so easily to me in high school, I could already read Cyrillic etc. and honestly that first semester of Russian was as much work as/almost as hard as that first semester of organic chemistry. And, after two years of that level of coursework in one of the most intensive slavic departments in the country, and not having taken German since my junior year of high school, ich spreche doch jetzt besser auf Deutsch als ich spreche auf Russisch (und ich spreche sehr schlecht auf Deutsch). Унзнать не-романские или -германские языки - очень трудно.
As far as specific experiences with Japanese, I have two friends who studied Japanese all through high school, both went to Japan, have taken at least two years of Japanese here, one of whom is majoring in Japanese and has been there multiple times and is actually currently spending the year there. They do pretty well in the Japanese program here/exceed what's expected of them.
My Japanese major friend basically told me when she took a semester of Italian (which isn't even Germanic like English) for S's and G's her freshman year she pretty much developed more conversationality in that language over the course of a semester than she did in 4 years of Japanese and multiple visits to Japan, one of which I think was for a couple of months.
It's just super super super hard. Not to be discouraging, but if you just try to jump in and learn Japanese on your own you're not going to get very far and that's going to be even more discouraging. Especially if you haven't previously developed multilingualism, learning new languages becomes that much harder. Especially if you're older, too.
Our local public library has discussion classes in Russian, Japanese, German, and several other languages I think, I'd look into finding something similar around you if you can, if you're interested in learning a new language.
