Turing machines with a finite number of states In a class on Turing machines, the lecturer said that the language for a machine with 100 states is both recognizable and decidable. 

How can we infer this just from the number of states in the machine?
You misunderstood your lecturer's claim. Their claim was that the language of descriptions of Turing machines with 100 states is decidable. The language accepted by each such machine need not be.

In other words, given a string, you can decide whether it describes a Turing machine having 100 states. That's the extent of the claim.