As we know, the Padawan braid was basically mandated as the 'sign of a learner.' But what about long hair (for a Knight) and a beard (for a Master)? Qui-Gon, Obi-Wan, and Anakin all had long hair during their phases as Knights, albeit at different lengths and styles. Qui-Gon and Obi-Wan (and now Luke) have beards (again, of different styles and lengths) as Masters. My question is, is there anything in the lore which suggests that long hair for Knights, and beards were mandated? Or is a matter of choice? Or did Obi-Wan simply grow his hair long, and then a beard, in honor of his deceased Master, and Anakin in emulation of his Master, and then Luke grew his beard to honor Obi-Wan? While a trivial matter, I am curious.
It's presumably just an age thing. Padawans are younger, so don't have facial hair until they've progressed to Kinghts or Masters once they're older. Not all masters have beards, or long hair, just look at Yoda or Mace.
I don't think Knights are really mandated to do anything other than generally obey the Council. They're not in a master-apprentice relationship anymore; they're pretty autonomous. (Anakin seems to be allowed to sleep wherever he likes without having to answer for his whereabouts, for instance.) The long hair thing is, I think, perhaps a matter of custom, but not required. Having longer hair serves to differentiate you from what you once were. It's a matter of personally carving out an identity for yourself more than anything, I suspect.
Many species who were Jedi have no body hair and so couldn't have beards or long hair even if they wanted to. So make these requirements would be 'species-ist'. Even as far as humans go, Mace Windu was bald so this theory crumbles.
I can't remember coming across anything in the EU or the new canon regarding grooming regulations for Jedi. I agree that it's down to both age and personal choice. From an aesthetic point of view, I think that the decision to have bearded and long-haired actors was very considered. Beards are often associated with mysticism and wisdom (think depictions of Merlin or Socrates). Therefore, beards would be appropriate for older, wiser characters such as Obi Wan in ANH and Qui-Gon. I think that Mace Windu, for example, was unbearded and bald because he had a very spartan personality. This suited his more no-nonsense style.
Just FYI. Apparently, Liam/Qui Gon's beard from TPM. ...was reused for Pierce Brosnan's character in Edgar Wright's The World's End. "Pretty cool, eh?"
So was it ever confirmed anywhere whether Liam's beard in TPM was all his / partly his / artificial? Liam looks like he can grow a full beard. I just recall Rick McCallum joking to check Algeria for it after the sand storm destroyed the Boonta Eve set, but I wouldn't exactly call this a reliable confirmation. This is a good opportunity to bring this up: Back in 2002 / 03 I distinctly recall there being two pictures of Samuel L. Jackson on the Geonosis Arena V.I.P. Balcony set, lightsaber prop drawn at Temuera Morrison and Jackson is sporting a beard in it. I assume this was only for staging purposes and he'd shave it off when going into make-up. Wish I had saved those pictures. Anyone remember them?
This is from 2012. He looks like he can grow a beard, much like Qui-Gon's. Qui-Gon's beard isn't the thickest; you'd think a fake one would be less patchy.
There was a hairstyle for Jedi rank, but it was on a different part of the body. Yoda and Mace followed it strictly.
The long hair for Obi-wan and the beard were more symbolic of Obi-wan being like Qui-gon, since he was his Padawan and it was designed to illustrate how far Obi-wan had come. The short hair of ROTS was meant to link to ANH and to show that while he was Qui-gon, he was also his own man. Dooku having a beard was also a bit of a nod towards the link between Dooku and Qui-gon. Anakin's long hair was a tie-in to the 70's look, but also that he was trying to emulate Obi-wan and Qui-gon. Luke having long hair and a beard is meant to continue that pattern. But it wasn't about requirements, since many of the human Jedi have one or the other, nor neither. The braid is the only element that carried on with most Padawans. Neeson confirmed in a 1998 interview for the "Star Wars Insider", that the beard and the wig were both fake and that he had reused them on different productions. He had used them on "Rob Roy", prior to filming TPM. McCallum wasn't joking about needing to find the beard in the 1999 interview.