Savage Species gives us some baseline LAs for the Large elementals, at least the 3.0 versions. We're looking at +6 for the Air one, +5 for Earth, +6 for Fire, and +5 for Water. Naturally, giving ECL14 to a CR5 creature is absolute nonsense, but the way the ECL scales is interesting - the first 4 levels give 4 hit dice.
Would I play a Small or Medium elemental at LA0? Let's just say that 100ft perfect fly speed or earth glide are worth a hell of a lot more than "make stuff wet" or "deal negligible fire damage."