Can a turing machine calculate word's length? I want to understand how a turing machine that will accept only words of length bigger than 100 will look like. 
My idea: it will copy a word and move to the right 100 times. 
If non of the cells was empty it will accept. 
Furthermore if it is true I can also conclude that it is decidable .

If there is no problem with my assertions so far, how will a turing machine that prints the number of letters in a word will look like? is it possible as well?
Replace every character in the input string with a $1$; you then have the length of the string in unary notation. Then convert the unary representation to your favorite base $b$ by successive division by $b$.