Learn English – Is this use of “have” correct

Why it’s wrong

Yes, it’s grammatically wrong. But your way of thinking about English grammar is right in a very profound way: wondering if singular and plural could be exploited to suggest some subtle distinction.

Here’s why it’s wrong. The pronoun their calls for a plural antecedent. Hair is singular. Also, movement is singular, so it has to be grammatically tied to an individual hair. If you tie it to the mass of hairs all together, then it suggests that the mass of hairs all together (what we normally call “hair” with no determiner) has one movement as a whole.

How to do it right

There are ways to use singular vs. plural to indicate what you have in mind. Here’s how you’d do it:

… each of his brown wavy hairs had a movement of its own…

The singular word each gives the singular movement something to attach to, and hairs is plural. This makes it clear that the sentence is talking about many movements, not just one.

You could also indicate separate movement of each strand of hair like this:

…his brown wavy hairs had movements of their own…

You are right that logic often trumps rigid grammar rules, leading a reader to interpret a sentence reasonably when too-strict application of grammatical regularity would lead to clumsiness. But since the language provides a straightforward way to indicate the intended meaning in this case, there’s no pressure to bend grammar.

The inevitable complexity

Their can take a singular antecedent when it stands for a person and you’re trying to avoid indicating “their” gender. However, to many people's ears, this usage sounds sloppy or ungrammatical, or at best informal, because their calls for a plural antecedent. There is currently something of a war going on in the language right now, to allow their to refer to a singular person as antecedent in order to avoid sexist language. Perhaps after that war is won, their will broaden to allow singular antecedents of all kinds, but today such a development is beyond the horizon.

If learning to drive is a short-term event that spans a few weeks or months, there's nothing wrong with saying:

My father learned to drive when he was 16.

If you want to emphasize, however, that learning to drive is more than a one-time event, that it's a never-ending accumulation of experiences and ongoing lessons on the road, then you would say:

My father has been learning to drive since he was 16.

If you simply want to emphasize how long he's been driving, then use the simpler:

My father has been driving since he was 16.

All three sentences reveal that your father first got behind a steering wheel at the age of 16, but they focus on three different aspects of driving: learning the fundamentals of driving, becoming an expert at driving, and just plain driving.

Now, about these two:

It is 5 years since I last saw her.
It has been 5 years since I last saw her.

Don't fall into the trap of thinking that one of these must be correct, and therefore the other must be wrong. I see that so much on the pages of ELL!

Sometimes one alternative is correct while another is wrong, but oftentimes both answers are correct, and it's just a matter of context: Are you speaking, or writing? Are you in New York, or in Sydney? Is the environment formal, or informal? I say lotsa things among friends that I probably wouldn't write in a research paper, and I've inserted many phraseologies into research papers that I would be highly unlikely to utter around friends.

I don't find any grammatical gaffe in either of the "5 years" sentences you wrote here (other than, in writing, we would usually write the word five instead of the numeral 5; we do that for single-digit numbers). However, your teacher's wording sounds too formal and stilted for casual conversation – at least in my opinion and according to where I live – so I'd probably default to your wording about 90% of the time.

As for getting some of your English lessons by watching movies, that's a two-edged sword. I'd be careful about that. On one hand, movies can give you a good feel for how people speak English in everyday life. On the other hand, not everything you read in a movie script is worth emulating. Movie directors want actors to say things in accordance with the characters in their films. So, if you watch too many mafia movies, you might end up speaking like a mobster. I don't think my wife would appreciate me saying, "Yo, Annabelle" – no matter how much she may have liked the original Rocky movie.