Mother language is English, and no, I didn't learn Chinese in 6-12 months. I studied 3 years in high school, 2 years in China, 3 years in college and another 2 years in grad school, so what's that 10 years all together.

High school was a wash, and living in China helped but I never made real progress till I hit upon this produce and repeat method. College and grad school were mostly classical Chinese and other dialects, so I'm not sure if that counts.

Were I to start Russian today, 6-12 months would be enough for a) no discernible accent and b) every day proficiency. But "pick up" is the wrong phase here. You aren't going to pick up a foreign language in 6-12 months with the immersion method. Look at what the grand OP did: 6-12 months of produce and repeat, followed by immersion. By the time he immersed himself, he had developed the faculties to process the stream of stimulus. That's a huge difference.