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: 'two people are holding their surf boards on the beach as they walk through the water'. Reverse all words of length '5' in the given sentence.

two people are holding rieht surf boards on the hcaeb as they walk through the retaw