Wow! Lots of interesting stuff in this thread!!
At 60+, I’m in the oldest 3% on this site. 
Nice to meet y’all!
In the late 80’s (in my 20’s), I studied basic Japanese for 2 years at a US University extension program. Classes were once a week, using Romaji textbooks (Eleanor Harz Jorden’s Beginning Japanese series anyone?). I came to Japanese language study through movies (Kurosawa, Ozu and the golden age of Japanese cinema), literature (mostly Kawabata and Natsume), as well as my interest in art/culture and spiritual aspects of the “Japanese way.”
Work and life took me in other directions in the 90’s, although I did get to Japan (Tokyo, mostly) a few times on business. I realized then that I didn’t want to live and work in Japan, even if I was fascinated with its culture, history, art, and people, in addition to being able to get by with my pidgin Japanese. However, I did want to spend more time there, even if I didn’t see a way to do it then.
Fast forward to 2014… Having recently retired, I stayed in Japan for 3 months and took up Japanese again on a lark (at GenkiJACS in Tokyo), just as a refresher and prep for further visits. I was placed in an intermediate class, where I just got by, well behind all the young kids there - the youngest was in his mid-30’s, whereas I was 55 - an 叔父さん, or worse, an おじいちゃん even! After the “final test,” which I managed to pass. The teachers said that it’d be a shame if I didn’t continue (as the teachers at GenkiJACS are wont to say to every student, I imagine). I did enjoy the experience, even if I was not sure whether to study further or not.
After I got back to the US, I took the JLPT 3 exam in 2015, letting the results decide whether I should continue to study or not. I passed by a mere 3 points. And so, 流れに身を任せ, I did a 3rd year course at a University here in Southern California, but quit after 2 semesters (see further on for reasons why). While studying by myself with a tutor for another year, I got an opportunity to teach practical/applied English at a University of Technology in Japan. Long story short, I accepted, and after spending 2 years to get used to the system and students, and having developed tech/business based Applied English courses, I’ve been teaching there one semester (4 months) each year. Even though it meant returning to a daily work routine, which I was not keen on, it has proved to be an excellent immersive learning experience.
In 2015, I had also started WK and was working at it at a sedate, leisurely pace. It took me close to 6 years to get to level 60, mainly due to 2, long 1000±day breaks associated with the teaching job. OTOH, since most students in my classes don’t speak/understand spoken English, I had to communicate with them in Japanese, which was just the right medicine at the right time! Over the past few years, my conversational ability has steadily improved. Now, I need to work on my reading and listening skills and pick up more grammar and vocabulary. I’d like to get to a point where I can read novels and magazine articles without difficulty and converse with native speakers in a professional environment at about 80% comprehension level.
The main issue that I had with studying at the University is the difference of my interests (broader cultural/historical vs manga/anime/etc), objectives (personal interest vs grade/job/etc), and the years of real life experience that I already had compared to the full time students. In addition, the 2-3 days/week classes with very little opportunity to interact in Japanese was definitely a drawback, even if the students were certainly quite good academically (i.e. at class room learning). The rote kanji learning approach was also a drag, but, I had WK for support. Looking back, I think immersion and full time language school are the way to go for older learners (like me), especially through a specific activity, or pursuit. Fortunately, in my case, it worked out pretty much that way.
Although age was not a deterrent when I started down this path, I realized that I am neither as nimble nor as quick a learner as I was in my 20’s or 30’s. As a kid, I picked up 3+ languages without much “studying” except for basics like alphabets and rudimentary grammar. Now, it is harder to remember as things are not as “sticky” as they used to be. OTOH, it is much more fun to figure out the language and its ties to the culture, through all the knowledge and experiences accumulated over the years in the many places and environments I had lived/worked in.
Oops… looks like I have been long winded. I better stop. 
By the way, a shout out to the 川柳 translation thread, started by @Rrwrex. In addition to being an excellent primer on the language, it provides additional insights into social and cultural peculiarities of Japanese and their way of thinking. The discussions are as valuable as the translation themselves. It is not just for poetry lovers, for sure. (I got to this thread through the 川柳 thread)