Your professor is correct. The length that one can achieve is mostly due to genetics. On average one's hair grows about three years prior to falling out and going into a short "resting" period. Then it begins to regrow. So "rate of growth" + "length of growth period" = "terminal length". Some people have much longer growth periods and/or faster growth, thus they can grow longer hair.

I've always felt that the health of my hair was more important than length.

I think most people's genetic potential is at least mid-thigh. Welcome to HB and nice to meet you Bibbles!

Anais

It sounds like your hairdresser is the reason your hair has been the same length for this long. 

Usually people don't hit terminal length that early...but the hair does have resting phases and one of them is around that length, (it can rest for up to 2 years) so it may sit there for awhile before it gets going again.  Stopping trims is not a good idea really if you want length.  At one point the breakage will equal the growth rate and that will make it look like you hit terminal length earlier than you might otherwise, though with a good hair safe routine, even that shouldn't happen until your hair is WAY long. (Also, a trim can be as small as an 1/8 of an inch and still be good for that purpose, so the reason yours is stuck sounds more like you're getting too much cut off).

I've seen so many photos of people with hair to their feet and beyond that I'm starting to think terminal length is a myth fostered by poor hair care routines.

Sadly, terminal length is no myth. The hair all over your body grows at about the same rate. The difference is in the terminal length. So for example, the hair on your arm only grows for so long prior to falling out and being replaced. Your arm hair goes through many cycles for every one cycle of head hair. Thank goodness the cycles of our individual hairs differ so there is always hair in all the places....can you imagine having no eyebrows for a period of time? Or, should I dare say..........no hair on your head during the rest period after every single hair falls out at the same time  

From everything I've read, on average mid to lower back is terminal length for the average person.

I personally think that some of one's head hair has a longer terminal length than some. Once mine reached tailbone length, I experienced excessive shedding and the ends got thin. I'm sure I could've kept growing, but I don't personally like thin ends on myself. So some of my hair might've reached a much longer length.

I agree with what some people mentioned above about trimming. I trimmed every 8 weeks during the whole growing process. But my stylist only took about 1/8" each time. She is great to work with. Since I'm basically maintaining the current length now, I get 1" trimmed every 6 weeks. (My hair is above my waist now.)

My hair would've looked horrible during the growing process without trims. Trims were essential for myself. Other people don't get trims, yet it seems to work for them. You have to determine what works best for you and your hair.

Patience is the most important thing. Once my hair reached about mid-back, it just seemed to take off and grew extremely fast. It was at my waist before I knew it (I had no intention originally to let it grow that long....it just kind of happened.)

Continue to keep it healthy and time will take care of the rest!

Susan W wrote: It sounds like your hairdresser is the reason your hair has been the same length for this long.  Usually people don't hit terminal length that early...but the hair does have resting phases and one of them is around that length, (it can rest for up to 2 years) so it may sit there for awhile before it gets going again.  Stopping trims is not a good idea really if you want length.  At one point the breakage will equal the growth rate and that will make it look like you hit terminal length earlier than you might otherwise, though with a good hair safe routine, even that shouldn't happen until your hair is WAY long. (Also, a trim can be as small as an 1/8 of an inch and still be good for that purpose, so the reason yours is stuck sounds more like you're getting too much cut off). I've seen so many photos of people with hair to their feet and beyond that I'm starting to think terminal length is a myth fostered by poor hair care routines.

A person can never simultaneously discover their terminal length and keep their ends neatly trimmed.

I'm seeking to discover my own terminal length.  I think I'm almost there.

Haircare habits can seriously impact one's growth potential.  If I used the poor haircare habits of some people I know (and read about), I might falsely conclude that waist-length (or something much shorter than I have) were my terminal length.

I know a woman whose hair is very fine and thin and won't grow much beyond shoulder-length, but she is the exception.  Many people who don't grow their hair long probably have no idea how long their hair could get (and might be surprised that theri own maximum length potential is a lot longer than they think).