Disclaimer: None of this is canon and this is merely a more in-depth description of Inkling/Octoling development. However, you may use these ideas in your fanfiction or art if you wish as well as modify how Octolings/Inklings brood their young.
So, here's a more in-depth age chart for Inklings/Octolings since the original only had five stages up to the teen years, this one has more than five stages and makes the growth look more gradual than anything. Featuring my Octoling Laleh.
0-1.5 years (18 months): At this stage in life, Octoling/Inkling babies have recently been born. Octolings/Inklings are ovoviviparous and mothers incubate their eggs inside their womb before they hatch. Once the eggs hatch, they give off a signal to the mother's womb to contract so she can give birth to the neonates. Neonates are mobile and equipped with a sharp beak and can eat solid food a few hours after birth but may have trouble finding food sources at this stage as they don't have a sense of direction at this stage and may get lost finding food, making them vulnerable to predation by larger animals or kidnapping by other adults. Instead, the mother will either store food somewhere before she gives birth or another adult will usually bring the mother food so she can regain the energy she invested in reproducing while sharing the food with her hatchlings. In terms of appearance, the newborns resemble an Inkling or Octoling in squid or octopus form but are around 1/2 as big to 1/3 smaller. Generally, it is difficult to distinguish biological sex (male or female) of an individual based on appearance alone at this stage. Many of them can make or imitate noises or sound effects such as whistling, chirping or barking, but they cannot talk yet.
1 to 2.5 years: The Octoling/Inkling grows a body, which is an extension of the mantle from the previous form. This body is typically as big as their head. At this stage, many Octoling and Inkling babies become more curious of their surroundings and will explore everything around them. Provision of opportunities for mental and emotional stimulation as possible is crucial to keeping them occupied. They will also begin crawling the same way human babies crawl and they can talk much like a parrot can, but some of what they say might not make sense.
2 to 4 years: The body has grown to be slightly larger than the head and the limbs have grown slightly larger. Octolings will begin to develop their ear pinna at this stage. Many Octoling/Inkling toddlers are more intelligent at this stage, but their inability to walk limits much of what they can do.
3.5 to 5.5 years: Inkling/Octoling toddlers are able to walk upright and their head tentacles begin developing. This is the age where traits of sexual dimorphism begin to show up in Octolings as Octolings who do not begin to develop their ear pinna by now are most certainly female. This is typically the age where they start preschool or kindergarten. At this stage they will watch teens and adults hunt and engage in combat, but are only permitted to observe and not participate.
5 to 8.5 years: Octolings/Inklings begin to develop their "hairstyles" and are already attending school at this age. They can begin learning how to use different weapons for target shooting but they cannot fight actual battles, not even in an educational setting. However, they are permitted to assist in hunts led by at least one legal adult or assist soldiers in the battlefield in menial or manual non-combat tasks (like bringing supplies from one camp to another). At around seven years old, many parents will also allow their kids to babysit, commute without an adult or teen supervising and be left home alone unless they have siblings younger than this age who need babysitting.
8-11.5 years: Octolings/Inklings can hunt for themselves, but only if they are supervised by at least one trained soldier. They can also participate in battles, but only in an educational rather than a competitive setting and only if one or more trained soldiers are supervising them. In educational battles, Inklings and Octolings typically all change into the same color to avoid actual damage to one another but they learn the techniques of how to ink turf and how to use weapons against opponents.
11-14.5 years: At 11 years old, Octolings/Inklings can make any adult decision or work any job with the exception of being able to fight turf battles so long as the family court considers them mature enough to make that decision or they have permission from their parents or guardians. They can hunt or participate in educational battles without the supervision of a trained adult soldier. However, until they are at least fourteen years old and are able to make the full transformation from cephalopod to humanoid form, they are not allowed to battle in a competitive setting. The ability to fully transform from cephalopod to humanoid can start as early as thirteen years old or as late as fifteen years old depending on the individual. Males also typically hit puberty at this stage and will begin to show interest in females who will often reject their advances.
