Actually studies show that adults learn faster than children.
The average time for an adult to learn a foreign language, if goes to 2 days/week classes, with classes of 60-90 min, homeworks, constant contact with the language via music or internet, will be 1.5-3 years. That's enough to go from zero to advanced levels, *if* the person is really dedicated to studying. One of the reasons I stopped teaching English was precisely that I could not condone with the lies so many language school use from "magical methods" where you learn effortlesly, to those that try to convince people they have to stay there at least 6 years.
A child will acquire fluency in their own language at an advanced level only in the early teens. And knowing your own language is a requirement to learn the new one. It's unlikely that anyone will be better in the foreign language. So children needs at least 12 years to be able to speak their own language fluently, and at least that same time for the foreign language.
The idea that children learn languages better or faster are due to two partial perceptions:
a) The one advantage children have over adults in languages is that since the muscles related to forming sound and the vocal cords are still forming, the have more *chances* of having less accent in the phonemes that specific to that language. For example, Brazilians have an extremely hard time with "th" pronunciation. I used to tell students it's just like learning a new movement in dance or martial arts: practice, practice, practice.
b) Demand and pressure on children is much smaller. They are allowed to commit mistakes and are not ashamed of doing so. Adults have much higher expectations and sometimes their jobs depend on it. So they are examined more closely and the cost of partial failures that are natural to the learning process may be greater.
I'm taking an elementary Russian class this fall. Any Russophones on the forums have any tips to start prepping?
This tip isn't language specific.
It has been shown that simply hearing a language without any attempt to make sense or mimic it for something like a hundred hours or so, will put you way ahead in the long run over those who spent similar time trying to "learn" the language.
Which makes sense. I hate when people talk about how more easily children learn a language than adults. Let's construct the same learning environment for both and I bet the differences shrink. Certainly, children have some advantages over adults, but adults have advantages over children as well.
Start listening to tons of Russian. Then again this is probably overkill for any University language class. They are rather facile.