Many factors enter into determining a person's terminal length.

Genetics plays a significant part. 

The care and treatment of the hair is an even bigger factor. 

Many people will say that they have a "short" terminal length.  Upon further investigation, it is usually determined that cuts, trims, chemical processing and the treatment of the hair is what is preventing longer growth.

A person's general health and stress levels can also affect hair growth.  Poor diet, nutritian, health can slow, even stop hair growth, or worse, cause hair to fall out.  Stress can do the same thing.

Hair grows in cycles.  Once a hair follicle has released it's hair, it may rest for a period of weeks to years before producing another hair.  Many people find that once their hair gets to about waist length, the growth can slow down even stop for a period of time.  This is called a resting phase. 

Long hair requires a lot of patience and gentle care.