Currently learning Japanese, honestly I think as adults we just go at it too formally
Kids babble, make mistakes get corrected and just soak up everything
Sure it might take longer once you are grown up, but if you don't have fun you won't be sticking to it
No problem. It helped me over my plateau with learning Spanish. I used a free CI app called Language Transfer. There are limited languages on that specific app, but comprehensive input 100% made it easier for me to learn the language as an adult.