The same baby turtles in 1976's Rocky - Cuff and Link - appear fully grown in its sequel 30 years later, Rocky Balboa.
So far, there are six Rocky movies all written by and starring Sylvester Stallone. Rocky Balboa was the last of the six films and takes place thirty years after the original Rocky, which makes it take place around 2005 or 2006.
In the first film, Rocky is 30 years old, making him born in 1945. In the final film, Rocky’s age is never specifically given, but he is meant to be around 60 years old.
The turtles, Cuff and Link, and were introduced in Rocky, where they were played by the same two actual turtles that play them in Rocky Balboa. Their significance to the Rocky mythos is that they formed the basis of the first bad joke which Rocky tells Adrian in Rocky.
They were their own special addition to the films. In the last film, Rocky only agrees to fight to prove something to himself and because he felt he had one last fight in him. The Rocky franchise is now officially over.