YOU CAN NOT USE "MIDDLE" FOR "LA MEDIA"
When Spanish speakers want to talk about the "la media" in English they often choose the word "middle" which, unfortunately does not work in English. We use "middle" when we are talking about something physical such as "a road": "Don't drive in the middle of the road" or "You need to cut the orange in the middle".
If you are talking about numbers then you need to use the word "average". So, for example: "The average age of people who go to a pop concert is 19" or "On average I get 100 emails per day".
Hope that helps!
Soy el director de Daniel Smith + Partners. Tengo más de 10 años de experiencia enseñando inglés a españoles.