I have very fine (i.e. thin-stranded)and fairly curly (especially if left to dry on its own) hair, which I have not had cut at all for about five years now. However, it is still not quite shoulder-length. For reasons irrelevant to this board, I am very stressed at present, which I am sure does not help, but the biggest problem seems to be that the ends get very tangled and either break off or get pulled out when I try to disentangle them. So far as I can see, the ends are not split, but do seem to narrow to a very fine point. Does anyone have any ideas:-
(i)Would it help to trim the ends? If so, should I try some sort of layering, or just leave every hair as long as possible, subject to trimming off the very thin bits, as I would hope that it would then grow to be of relatively uniform length but below the shoulders?
(ii)Does anyone know of a strengthening agent which does not make tangling even worse?
I don't have much experience with thin hair. Nevertheless, I will make some comments that may be relevant.
If the hairs break off they will not narrow to a fine point. They can, however, if they split off. If you don't have split ends, I think it's unlikely they are splitting off.
A couple things you mentioned lead me to belieave you are seeing the natural ends of your hair. You said you've been growing 5 years without a cut and your hair is only shoulder-length or less. This tells me that your hair is falling out at this length. After hair falls out, it grows back out again. However, since it is "recovering" from a rest stage, the diameter of the shaft starts out very small and gradually increases.
Help for what? It would not help your hair to grow longer. It also will not help keep it from breaking (IMO) if you are not getting split ends. Without split ends, trimming is entirely cosmetic.
The best thing to strengthen your hair is to have a well-rounded diet and a stress-free life. For the stress, I suggest something along the lins of this quip I once heard:
A man, in order to reduce work-related stress in his life, decided that when he arrived home, he'd hang up all his problems just outside his house. They would wait there until he was on his way to work again when he would pick them back up. Meanwhile, at home, he'd worry not at all and simply enjoy his family. Miraculously, every day he went to work, he picked up less than he dropped off upon entering the house.
I'm sure all this can be worded a lot better, but you get the idea. Regarding tangles, I suggest you try using Pantene spray-on detangler or Citre Shine hair polisher. These two products work to detangle hair better than any other I've tried so far. I can't vouch for your hair type, but it can't hurt to try.
On a final note, I suspect that you may simply have a fairly short maximum hair length. There may be nothing you can do about it. I have a friend (female) who has this same feature. Her hair never gets longer than about shoulder length.