In Naruto Trying to become a Saiyan from Kumogakure

Children grow through several stages, each marked by distinct milestones. Infants (0–1 year) rapidly grow physically, develop motor skills, and form emotional bonds. Toddlers (1–3 years) begin walking, talking, and expressing strong emotions. Early childhood (3–6 years) brings imaginative play, social interaction, and improved coordination. In middle childhood (6–12 years), kids experience steady growth, develop logical thinking, and deepen friendships. Adolescence (13–18 years) is characterized by puberty, rapid physical changes, abstract thinking, and identity exploration. Each stage reflects a unique blend of physical, cognitive, emotional, and social development.

Kids born from ninjas typically start walking and babbling when they are around 1 year old, they reach the teen stage at 5-6 years old, and during warring state periods where ninjas existed as clans and rouge, taking tasks without discrimination, causing numerous conflicts with wars being the constant theme of time, children's of age 5-6 went to battlefields and started families in their 10s, clearly showing rapid growth on ninjas compared to normal humans, as even a genin the lowest level of ninja can overpower a grown man, of course, that's just civilian ninjas, people like Might Guy and Lee who can smash trees with just a kick in their youth are beyond what a normal human can do despite being civilian ninjas.

In the Chunin exam on Naruto, Rock Lee was wearing weights beyond what a human can withstand and that is just his physique, although ninjas can use chakra to enhance themselves, Rock Lee could not have been using chakra constantly while training, and in the 5 days of the 2nd phase of the Chunin exam, where if he distracted himself by taking on and off the weights his team could have been ambushed, it's not like he is a jinchuriki or like Naruto being from the Uzumaki a clan known for their huge amount of chakra.

This raises a broader question are ninjas truly human as we understand them? For ninjas, chakra is something they are born with, but maybe they are not humans to begin with, just as normal animals and summoning animals that use ninjutsu are different! Just the amount of cells in the body of these creatures differ from others, due to their huge size. You know on Earth the cell size of a human and a Whale is the same, it's just they are made out of different numbers of cells. If a human is scaled to a thousand meters like some huge summoning beasts, their cells would be about 12 millimeters, creepy to look at, and size unstable for cells, as evolution caused all cells in animals to be about the same size.

But in the Naruto universe, this is not true and even the cells' number and sizes vary depending on different ninjas especially ninjas with bloodline limits also known as kekkai genkai's exhibit hereditary abilities that can alter their biology within a single generation, bypassing the gradual process of natural selection. Chakra not only shapes their abilities but may even influence the size and number of their cells, allowing them to perform feats that defy scientific norms. This unique manipulation of biology and evolution through chakra underscores the Naruto world's divergence from natural laws, creating a realm where the impossible becomes reality. After all, chakra was initially from an immortal species, that can constantly evolve and grow from plundering the worlds, known as the Otutsuki Clan! Chakra is magical in the Naruto world as Pain can even manifest technological abilities, by shooting rockets from his puppets, and it can interact with the physical realm and even the soul.