I've been asked what is terminal length for hair, here is what I have found:

Terminal or Maximum hair length

A person’s terminal or maximum length will be determined by several factors:
1.  Average growth per month
2.  Average hair loss/molting each day
3.  General health of the person
4.  Age
5.  Gender
6.  Hormonal balance (pregnancy, menopause)
7.  Hair type
8.  Hair condition

The average hair growth is ½ inch per month for women, a bit less for men.  People living in warmer climates might experience more rapid growth.  Genetics also play a role in monthly hair growth. 

The more hair you lose each day, the fewer hairs that are available to reach longer lengths.  This loss is referring to hair was shed from the scalp and not a broken hair.  The longer the hair stays attached to your head, the longer the hair can get.  When a hair is shed, that follicle will rest before producing a new hair.  The fewer shed hairs, the more hair you have on your head and the longer the hair itself can get.

Poor health, nutrition, stress, etc can weaken the hair follicle causing it either grow slower or fall out.

Women’s hair grows fastest between the ages of 16 and 30.

Hormone changes play a significant role in hair growth.  Puberty seems to be the start of a person’s most rapid hair growth. Pregnancy typically brings on rapid growth (with significant shedding after the birth).  Menopause frequently brings on slower growth and more shedding.

The more hairs you have on your head, the higher the likelihood your hair will grow longer. 

Hair in good condition is less likely to split or break, allowing it grow to its maximum length.

[Reference:  The Hair Grower's Handbook