Meat for humans can be stored in a freezer for up to about a year. It is still safe to eat after that, but the quality is lessened. Maybe I wouldn't eat 2 year old meat from my freezer, but it's because I am picky about quality, bot because it is unsafe.
There was a mammoth found frozen in Siberia that was sampled by humans.
http://pao.gsfc.nasa.gov/gsfc/educ/s.../11-04-99.htm, This would have been at least 8000 years old, and possibly a lot older.