If you have a context for this,
"eles / elas" can refer to animals, people or objects. Noting that the gender rules are apply on these cases as well.
The pencils are white. (Os lápis são bancos) = Eles are white.
The gold spoons (As colheres de ouro) = Elas são de ouro.
Oh, oops. I meant to reply to your comment. What I said wasn't exactly clear. I meant that I agreed it should be "baixo" for people because short almost always refers to height with them. But in the event that "eles" refers to pencils, as Diogo suggests, the pencils could be short, and I think that would be "curtas", right?
Exactly, pencils would be «curtos»; animals, however, would be «baixos». In English, "short" is too general; it can either be the opposite of "long" or the opposite of "tall." In Portuguese, the distinction is clearly made, with the opposite of "long" being «curto» and the opposite of "tall" being «baixo». :)
I've seen both 'eles' and 'elas' used for 'they', but there seems to be no pattern as to which one is appropriate in a given sentence. Sometimes 'eles' is right and sometimes it is wrong. I suspected it is like 'obrigado' and 'obrigada', used depending on the gender of the person speaking, or perhaps the gender of the 'they' being referred to, but now I am not sure. When should 'eles' be used as 'they' and when should 'elas' be used?