A lovely essay in the Times about older women having long hair. (Bonus: She mentions the no-'poo technique at the top of the second page!)
It's interesting to think of our older sex symbols (I really, really don't ever want to hear my father say the words "Helen Mirren" again, but of course the woman is incredible) and see that whatever physical attributes they may possess that land them in that category in the popular mind--sultry features, a certain grace, a conspicuous absence of fat accumulation around the middle--long hair isn't among them. The door is the tiniest (tiniest!) bit open for us to think of older women as sexy--I suppose it's the one upside of the whole "cougar" thing--but, despite the very agency that these women have that makes them so appealing, there are certain things that we collectively expect women to give up. We shift our definition of sexy to include a very select handful of women of a certain age, but even there the Iron Maiden prevails; there's not enough space around the head for long braids, or a ponytail--if you want in, shoulder-length is the most you can hope for, even as your above-the-knee skirt reveals a shapely calf and your smile lines belie your temperament.
The long-haired women over 50 I know--my flame-haired mother included, not a gray hair on her head--may have beautiful hair, but there's also an air of rebellion about it. I find that the women who have long hair at that age are also less likely to do the extreme sort of things that less self-assured counterparts might do--plastic surgery, an overuse of makeup, etc. So I don't know if the rebellion is because they're saying to hell with trying to look younger (but look girlish anyway, tresses flowing), or because of the juxtaposition of a slightly weathered face and bouncy hair, or because they're simply doing as they please. But in any case, regardless of the sex appeal of long hair, rebellion can be sexy as hell too. Cougars they might not be, but I salute the long-haired lionesses among us.