Is over exercising related to eating disorders? why?

In my opinion, no, over exercising isn't related to eating disorders.
However, eating disorders can be related to over exercising.

For example, someone may just be very active and play lots of sports or workout a lot. However, this doesn't necessarily mean that this person doesn't eat well. 
As for my second point, eating disorders ARE related to over-exercising because depending on the person's situation, it may be linked to their goal to lose lots of weight, as this is another way to do so. 

Hope this helps!

Yes, because in certain eating disorders such as anorexia where a person thinks that they are too fat don't eat enough and over excercise

The answer would be age 18.