Googling this: "law minor energy drink" shows that many places are considering it, although I have not seen any that actually passed such a law.

In Russia, "energy drinks" are forbidden for minors (< 18 years), but coffee, tea and coca-cola-like drinks (which AFAIK can have caffeine too) don't have such restriction.

Dosage and sweetness is surly part of the rationale. Coffee is not a cool, sweet, refreshing drink. Soda is but has around 50 mg of caffeine, while energy drinks have between 80-160 mg. Probable harm from high levels of caffeine much easier to hit with energy drinks.