Well what do we have?
"(...)When those twain were at table he had taunted him oft,
lightly with laughter, for his loveless ways,
his haggard raiment and hair unshorn;
but Turin untroubled neither turned his head
nor wasted words on the wit of Orgof.(...)"
I guess we can read this passage as an evidence that In Doriath shorter Hair was more common, and Turin stood from the other males out for having longer, wilder and unkempt hair.
"(...)Vana, repenting of her past
murmurings, cut short her golden hair and gave it to the Gods,(...)"
"(...)the endless hair of Uinen(...)"
Among the Ainur Varda, Vana and Uinen are all described as having very long hair (especially Uinen). Again we could read this as an evidence that the other Valier had shorter Hair... but its interesting that here the reason for Vana cutting her hair seems to be repentence...
"(...)one came unto Tinwelint, and Tinwelint
knew him not for the wild growth of his hair -- and lo! it was
Mablung(...)"
Mablung was out in the wilds and couldn't comb and cut his hair so he had the unkept look, like Túrin,
but oviously again that look was not comkmon at Elwes Court at the Time. Maybe Sinda Men generally wore their hair shorter.
"(...)Faiglindra 'Long-tressed' (Airin). Gnomish faigli 'hair, long tresses
(especially used of women)'(...)"
Well so Airin wore her hair long tressed and long tresses were generally more associated with women...
"(...)faiglion 'having long hair', and
faiglim of the same meaning, 'especially as a proper name',(...)"
On the Other Hand people are rather named after uncommon feats than after common ones... so if somebody is called Faiglion or Faiglindra, maybe their long hair is regarded as outstanding?
"(...)There a shining shingle on that shore lieth,
whose pebbles as pearl or pale marble
by spray and spindrift splashed at evening
in the moon do gleam, or moan and grind
when the Dweller in the Deep drives in fury
the waters white to the walls of the land;
when the long-haired riders on their lathered horses
with bit and bridle of blowing foam,
in wrack wreathed and ropes of seaweed,
to the thunder gallop of the thudding of the surf.'(...)"
I'm not sure if this line is about the Foamriders, Elves, or Ulmo#s people, Sea-Spirits...
"(...)the folk of Faerie in the first noontide
of the Blissful Realms; with their brows wreathed
in garlands golden with their gleaming hair
in the wind flying(...)"
Well here flying hair is mentioned for the Folk of Faerie (Ainur, Elves or both?), to fly Hair has got to have a certain length
"(...)Turin still seizes
Brodda by the hair,(...)"
So the Easterling does seem to have somewhat longer hair... but it doesn't have to be very long (I have short spikey hair and it#s quite possible to grab me by the hair)
"(...) Elwe was their lord, and his hair was
long and white.(...)"
So while many Sindar of Doriath might not have had very long hair, Elwe in fact did.
"(...)Then Celegorm arose amid the throng (p. 169). In QS this is followed by
'golden was his long hair'. In the Lay at this point (line 1844)
Celegorm has 'gleaming hair'; his Old English name was Cynegrim(...)"
Celegorm also has long hair.
"(...)The hair of Olwe was long
and white,(...)"
Olwe also does..
"(...)In the case of Fingon it was suitable; he wore his long
dark hair in great plaits braided with gold.(...)"
like you mentioned... interesting are the plaits braided with gold! Could inspire some hairdos...
"(...)But most it was
their (the Teleri) wont to sail in their swift ships upon the waters of the Bay
of Elvenhome, or to walk in the waves upon the shore with their
long hair gleaming like foam in the light beyond the hill.(...)"
So the Teleri of Elvenhome generally wore their hair longer...
"(...)They (Galadriel and Celeborn) looked tall even as they sat, and
their hair was white and long.(...)"
Also Celeborn has long hair, seemingly as long as his wife's.Again this could be read as evidence for both having longer hair than the common elves of their realm.
"(...)lo! there stands Idril before him with her hair unbraided(...)"
So more commonly Idril seems to have worn her hair braided.Idril, lúthien and Airin are all described as having long hair, other elf and Edain women are not explicitly known for long hair.So what does this mean to us?
After all we just will have to decide what long or short or shorn hair does exactly mean ... there are points for Elves having long hair in general, but also points for long hair being mentioned because it was rather uncommon, or a special trait not applying to the common everybody.
. Jenny Dolfen nearly always depicts Fëanor and Maedhros with short hair (though her Maedhros-in-Valinor tends to be long-haired). She has her own little story for that in her illustrations. As long as we have reasons for our choices, we don't have to make the obvious/typical choice.
