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: 'several people are on an open beach while a kite flies in the blue and lightly cloudy sky'. Reverse all words of length '7' in the given sentence.

lareves people are on an open beach while a kite flies in the blue and ylthgil cloudy sky