The same story as the movies. Requested to be GAR and cloned from Jango Fett, a Mandalorian Bounty Hunter.
There were original Jango clones and then a group of enhanced clones called the Proto-class clones.
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(Above is Jango Fett, Mandalorian Bounty Hunter)
CLONE ANOMALIES
As Jango's DNA got stretched more and more, the differences in clone appearance did as well as voice changes. And when Jango passed, more DNA was taken from Proto-class clones which resulted in slight enhancement (see PROTO CLONES chapter).
CLONE GROWTH
Toddlers
In toddler care from years 0-2. They focus on brain stimulation to respond to commands and to discover strengths early on so that the potential captains and commanders and ARC soldiers can be picked out early.
Cadets (pre-teen)
Clones are in the cadet phase from years 2-6. Though maintaining physical endurance, most of their training was focused on intelligence and classes.
Classes included Languages (such as Mando'a and other prominent tongues), Strategy (ground battle, space battle, etc), General Geography (to cover scientific processes of planets), Galactic Geography (covers the maps of stars and systems), Weapon Maintenance, Vehicle Maintenance, Piloting, Medical Procedures, etc.
From there, star pupils will be spotted and brought into further training if they are exceeding in certain fields. For example, Rex was spotted in his early cadet stages as a potential captain and put into deeper training.
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Cadets (teen)
Clones are in their teen phase from years 6-8. At this phase of their growth, they grow from preteen to young man in just two years time which is an extremely painful process topped onto the extreme physical fitness they go through to become the best soldiers in the galaxy.
They go through drills, also learning to interact with their fellow squads more closely. This is where the most changes develop in the clones. And with teenage rebellion forced into two years, it's also the most difficult stage to control so the hired bounty hunters can best interfere with little attachment since the clone leadership can get attached to their brothers.
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Soldier (young adult)
At their stage of young adulthood, it is drawn out from age 9-16. Whole squadrons are chosen to join a legion by their Jedi leaders and clone commanders/captains.
Clones often will get tattoos and dye their hair to differentiate between each other even though they have grown to look somewhat different due to DNA mutations from the thinned DNA strands that remained from Jango.
Below you can see 4 clones side by side to see their resemblance and differences.
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Soldier (adult)
Clones reach their adult stage from years 16-25. As the soldiers age, they either go up in rank, or slowly transition out of fighting.
Retired (elder)
Clones reach their elderly stage at around years 25-35. Not much is known about the life of a retired clones since they have yet to reach this stage.
