Yog Sothoth said
in the show, genin can be pretty powerful, look at Rock Lee, Neji and Sasuke. genin really is just a rank and doesn't always mean weaker than a chunin, some genin can learn really fast when it comes to some techniques.
Neji and Sasuke are geniuses. Every character is NOT a genius.
Sakura, Ino, Ten-Ten, Kiba, Choji, Shikamaru were Genin level when they were Genin. You are comparing genius character's with characters with pretty usual/typical bios and assuming that they are all geniuses. That's unrealistic.
Saying "My character learned the techniques at a young age" is only reasonable to a degree. I can't exactly talk, having a Genin with an extremely high level technique myself, but even Genin from powerful, prestigious clans start off fairly ordinary. They aren't using Jonin level techniques just because. Which is the case here. It still takes many years of training, practical experience, and keen intellect to utilize techniques like the Yin Healing technique, which is something even Tsunade was surprised about. It's like being a doctor, 10 years of schooling, simply because you were "trained at a young age" thus at 15 years old you can perform open heart surgery.