@Bold: Yes, and that's exactly what Sarada is doing isn't it?The literal definition of the term "prodigy" is a person who performs feats at an age younger than 18 that are supposed to be feats only an adult can do or even surpasses an adult who is an expert in that field under normal circumstances by such individuals
No one else calls Boruto a Prodigy based on feats because we have no idea, or we are unclear of what he does, but we do know that what-ever Kishimoto hailed him for as Prodigy, meets the criteria for the word itself.
For instance, if Boruto created the Lightning Rasengan, where Kakashi/Minato failed (who are Adults). It is labeled as a Prodigy, someone who is prodigal.
You say not everyone can reach Sakura or Tsunade's level of chakra control but that in itself is fan fiction when the only person who had tried was Shizune and she also came from no clan what's so ever, she just lacked what Sakura had. Never was it stated that Shizune was some sort of medical shinobi Genius or Prodigy in the arts or had a mastery of chakra control.
Hell, wasn't even it stated in the DB that Shizune taught Sakura all she knew anyway? <--- OOC question
And yea we are not calling Boruto a prodigy based on feats because we haven't seen them yet, but we've seen Sarada's, and for an academy student doing what she did is definitely prodigious.
@Bold2: lol what? It's not fan fiction, it's manga fact, they are the only ones who achieved it. Doesn't matter if we know how many people tried (we don't actually, although I'm sure there are plenty of medical nins aiming for it in NV), it's still the epitome of CC.