Definition: In this task, you need to reverse all words of a given length in the sentence. The number of letters in a word determine its length. For example, the length of the word "apple" is 5.
Input: Sentence: 'people standing behind a fence watching two horses being led up a dirt path'. Reverse all words of length '6' in the given sentence.

elpoep standing dniheb a fence watching two sesroh being led up a dirt path