Periodization is retrospective, meaning that we divide history into periods after the fact. There is nothing inherently middle aged about the middle ages. A person living in, let's say, 1000 CE, wasn't aware he was living in what would later be called "the Middle Ages". He lived in "yesterday, today and perhaps tomorrow". The term is a renaissance term, initially used by the people of the renaissance to describe the middle period between what they perceived to be the pinnacle of humanity -- Classical Greece and Rome -- and themselves. Furthermore, periodization differs from place to place.

We typically use the fall of the Western Roman Empire in 476 to mark the beginning of the Early Middle Ages in Europe.

Now, where I'm from -- Norway -- we still hadn't left the Iron Age at the time of Rome's fall, and we traditionally use the death of the last Viking king, Harald Hardråde in 1066, to mark the beginning of the Early Middle Ages, and the end of the Viking age, instead. In the rest of Europe, the Viking age goes neatly under the Early Middle Age period, however.

I'm on a phone, but I hope this clears some of it up.