Hi Alison

I think at 22 you are much too old and you have zero chance of ever learning J

Rubbish! Of course you can learn Japanese! And Arabic and French and Spanish and Thai and Bahasa Malay if you want!

1. Here's a website by an Irish guy called Brendan (Benny) Lewis (actually I didn't know until now that he comes from quite near me) and he sets himself a goal of learning a new language every few months.  http://www.fluentin3months.com/about/; and here's a report on his level of Mandarin after three months. 
    
2. Here's an interview with a well-known polyglot based in Bangkok, Stu Jay Raj
     
3. The post "How to learn Any Language 3 Months" in has a few sensible tips - decide what to learn, based on usage frequency (priority); filter materials based on your likelihood of continued study and review, or adherence (interest); finally, decide how to learn the material most efficiently for you. (process).

   These are all specific to individuals and their interests - the same language class or method does not work for everyone. Sounds a bit boring, but logical.

My one tip would be to learn Japanese not just to learn Japanese, but to learn for a particular reason, e.g. to sing like a particular star or to to learn a martial art or to be a branch manager in Daiso or because you want to collect antiques from a particular period or because you want to write poetry...Your interest in the reason will push you past the difficulty of learning the language.

Good luck! Maybe you can start a Japanese version of Writefix!