My last year at the academy and I was finally able to start practicing this technique. The sage Body Technique is a way of exercising your body while you're tempered by the natural energy of the environment first and foremost you need to follow the normal steps someone does to become a sage.
First: you need to be stable and unmoved, absolutely still.
Second: you need to feel the natural energy all around you.
Third: you must absorb and balance the natural energy with your chakra. (that is the easy part for me as I have Mokuton I'm already part of nature so this part is just to reach the correct ratio).
After completing these steps you will be able to enter the sage mode, the speed, and situations you can enter this mode change depending on how much proficient you are.
But the Sage Body use this principle of absorbing the natural energy while I make physical exercises to temperate and clean my body, making my body slowly transform and strength itself and the best part of it is that this is an extremely natural process, so I can even use this technique this young, I just waited this much because you need a certain foundation to practice this technique. After all, it's extremely tiring to your body and mind so you need to be fully prepared for it.
Now talking about its benefits.
First: After a certain degree of proficiency The practitioner of This technique Stop aging.
Secon: Your body became like a part of nature so you're practically undetectable by normal sensing means.
Third: All around boost of the body and techniques without the necessity of entering the sage mode, this technique is the equivalent of making your body always be on the Sage mode.
Four: the technique is evolvable but, be warned, you need to put your body to the limits while practicing this technique, or your results will be minuscules.
Five: For extremely experienced practitioners of this technique you will be able to enter on a state of overdrive that causes extensive damage to your body but making yourself many times stronger.
Six: Practitioners of this technique are often overloaded with the YANG attribute so be warned to Always try to Accompany its Rise With your YIN side.
Seven: To reach the Six Path Mode(Liquid state) you need to enter a certain Mental State so don't expect to train only this technique and become a god. (AN: yup I was surprised of this too, so apparently Naruto's six Path Mode is a Mental state that Rikudou helped him achieve, this mental state is necessary to make Godoudamas and all that funk they do on the final fight, so I decided to put these mental state point in my fic too, is extremely easy to just put a Juubi and Rinnegan on to yourself to reach such stage but I will try to create a believable way for our mc to reach such a stage with his own efforts).
Starting training I spent at least a week to be able to use the normal sage mode, two months to be able to move normally while I absorbed natural energy, on the third month I was already able to do some light exercises while drawing energy, on the fifth month I was able to do everything normally while using the technique, and on the sixth month, I was already able to use Jutsus while training the technique. Now using and not using this technique doesn't make that much of a difference in my control or behavior.