Cat Ages Based on Human Milestones
Warrior cats age equivalents has always been a very sketchy and confusing thing. Many people often just do a linear cat to human age, ex.: 1 month = 1 year, but I've always believed it isn't so straight forward and that warrior cats' age physically and mentally different.
I think the best way to determine a cat's age in relation to a human's age is based on milestones, such as when a toddler takes their first steps, or a kitten first starts eating wet food.
But, as you'll see, there are discrepancies in doing this. For example, humans are often walking better before they're weaned off milk/baby food, while kittens can often be weaned off milk before they're walking without wobbling. Additionally, cats can become sexually mature very young (child age), while that is more rare in humans (though not impossible).
Cat maturity has a different "system" than human maturity, so this is just a close equivalent to help some people visual the ages better.
Cat age = Human age
3 weeks = 2 years - 3 weeks is when weaning off of milk and onto wet food often begins. Similarly, 2 years is considered the "cut-off" for babies breastfeeding. Capable of talking at this point, though communitive abilities differentiate
4 moons = 10* years - cats can become sexually mature at 4 months of age. Generally, afab persons can start puberty at 10 years and technically be "sexually mature"
6 moons = 6* years - when apprenticeship starts is akin to when first grade starts, but I'd personally say 6 moons old feels more akin to a 9-10 year old (4th grader) to me and 4 moons old are the 1st graders, especially considering the next age and context of "sexual maturity"
7 moons = 12 years - most places consider cats "adults" when they are seven months old, as they are mostly done growing. 12 years is generally when puberty begins, so it's technically the opposite (start growing)... but in ye olden days, you could be considered an adult at 12 so. It's the closest equivalent if we are keeping 12 moons = 18 years.
12 moons (1 year) = 18 years - both are when they are considered independent "adults" in their societies
84 moons (7 years) = 40-50 years - 7 years is the "senior" status for cats, when they're "old" adults. Most people call 40 year old's old
120 moons (10 years) = 60-70 years - the "retirement" ages
216 moons (18 years) = 100-110 years - 18 years for a cat is like living past 100 years for a human. Though it should be noted wild/stray cats do not tend to live as long as indoor cats, so this is especially a "rare" age for warrior cats
Based on these milestones, I would put the warrior cats aging as....