A lot of what a cat's emotions, personality, and physical traits are related to their age. However, cat years are different in human years. 

This is a list of cat/calendar years to human years. Basically, it's how old a cat would be if it was turned into a human.

Kitten
1 month old cat = 1 year old human
2 month old cat = 2 year old human
3 month old cat = 4 year old human
4 month old cat = 6 year old human
5 month old cat = 8 year old human
6 month old cat = 10 year old human

Junior
7 month old cat = 12 year old human
12 month old cat = 15 year old human
18 month old cat = 21 year old human
2 year old cat = 24 year old human

Adult
3 year old cat = 28 year old human
4 year old cat = 32 year old human
5 year old cat = 36 year old human
6 year old cat = 40 year old human

Mature
7 year old cat =  44 year old human
8 year old cat = 48 year old human
9 year old cat = 52 year old human
10 year old cat = 56 year old human

Senior
11 year old cat = 60 year old human
12 year old cat = 64 year old human
13 year old cat = 68 year old human
14 year old cat = 72 year old human

Super Senior
15 year old cat = 76 year old human
16 year old cat = 80 year old human
17 year old cat = 84 year old human
18 year old cat = 88 year old human
19 year old cat = 92 year old human
20 year old cat = 96 year old human
21 year old cat = 100 year old human
22 year old cat = 104 year old human
23 year old cat = 108 year old human
24 year old cat = 112 year old human
25 year old cat = 116 year old human

Facts:
• Cats with a corresponding human age of 0-18 are in the growth stage.
• Most kittens become adult cats at 1 year old, however most Maine coons reach adulthood at 2 years.
• Certain cat breeds besides the Maine coon have a very specific aging profile that is not captured in the list above.
• The longest living cat was called Creme Puff, who was born on August 3rd, 1967, and lived until August 6th, 2005 - an amazing 38 years and 3 days old! If that followed the trend of plus 4 human years every cat year as a senior, Creme Puff would've been 168 years old as a human, surpassing the oldest living human, Jeanne Calment, who lived up to 122 years old.