I think it's similar to the average age at which people die. These days the average age that people die at varies around 70-80 in modern countries with 60, 50 or less in less modern countries. It of course doesn't mean that people simply have to die at 70, as there are some that reach 90 and even 100 and go on.
For instance I believe that asari in the game live up to 1000 years, but it doesn't automatically mean that they live exactly that much. Some can die before 1000 other surpass it... at least in my opinion.
They use universal Translators, Although they only explain it in the book's.