Beards (Mine hasn't sprouted yet : ( , I'm only 12)

[Sharkû]

"But the shapes wherein the Great Ones array themselves are not at all times like to the shapes of the kings and queens of the Children of Ilúvatar; for at times they may clothe themselves in their own thought, made visible in forms of majesty and dread." (Ainulindale)

"The dealings of the Ainur have indeed been mostly with the Elves, for Ilúvatar made them more like in nature to the Ainur, though less in might and stature;" (Silm. 1)

"But the Quendi shall be the fairest of all earthly creatures, and they shall have and shall conceive and bring forth more beauty than all my Children;" (ibid.)

Furthermore, we know of the ambivalent relation of Valar and Elves with Men.

" His [Tulkas'] hair and beard are golden, and his flesh ruddy; his weapons are his hands." (Valaquenta)

So: a) The Ainur looked like Elves and Men
b) The Elves are more beautiful and like to the Ainur
c) The Ainur in turn lean more towards Elves
This leads to: => d) it can safely be assumed that the Ainur took rather the form of Elves (cf. also Olórin) than that of Men
e) Tulkas had a beard
Together with d), e) leads to f) (less likely, but an interesting speculation) Tulkas was a friend of Men, of the Valar the one most concerned about them and/or g) beards were thought to be beautiful and/or h) beards were common enough among Elves even in the vision of things to come the Valar only had in the Ainulindale.