I learned French when I was around 41 or so. I don’t know how fluent I was, but I was able to speak and understand it fairly well when we traveled to France.
I took no formal lessons; I got the “French in Action” series of videotapes plus textbooks and studied the hell out of them. Mimicking Professor Capretz from the videotapes gave me a good accent. I’m pretty sure the technique used was immersion, as no English translations were ever provided. It worked pretty well.