Dennis King wrote:
rlivingston1488 wrote: 

    Is there anything in the mythology of Ireland that places significance on
the wearing of grey wool on your chin during a battle?  Does it simply
disguise you?  Does it scare your opponent?  Does it imply that you are a
learned old man who will use his cunning to defeat his opponent rather than
his strength?

There are instances in OI lit. of beardless young men (Cú Chulainn 
in the Táin, Néide in the prologue to I2T) who put on fake beards
in order to make themselves fit for combat in the eyes of others.

This looks like another instance of the same story-telling motif,
but with one-upping of the degree of maturity/competence by making
the beards grey.

I agree--beardlessness seems to have been equated with immaturity and weakness. I have a copy of an unpublished paper, "Ul na n-Ulad," by Patrick Ford, in which he cites several examples of Ulster warriors' beards being describedor mentioned when the warrior himself was being described in positive terms.  Interestingly, Pat points out that "there is no mention of beards on any of the warriors who came against the Ulaid in Táin Bó Cuailnge."  --Kathy