On a related note: Я "коренный" американец и мне исполнится 40 лет в ноябре. Can I call myself an ученик русского языка, or must I say "я -- учащийся русского языка"? And what if the topic is not a foreign language, but gourmet French cooking or Japanese martial arts? Can I say "я -- ученик карате" or "я -- ученик французской кухни"?

P.S. As Alexsms correctly observed, "student" is used very broadly in US English -- so no matter how old you are, it's okay to say "I'm a student of English" or "I'm a student of karate" or "I'm a student of French cuisine." On the other hand, "pupil" in the sense of "one who is learning" is used rather rarely in US English, except when talking writing in formal contexts about "elementary school" (children younger than 10-12 years old). To Americans, the normal meaning of "pupil" is "the black part of the eye."