Proper Way to Prompt To Return A Specific Number of Words Response

Background
Using API call with GPT 3.5 Turbo and have the following in the Prompt passed via Endpoint

“Mike is 14 year old boy who builds a robot. The robot can speak and is made of wood. They become friends and go on adventures. Create a response in the language of English. Response should be written with a flesch-kincaid score grade level of 8”

This prompt returns a response of 195 words

If I change the prompt and ask for 1250 words, I get a response with 852 words

Here is the new prompt:
“Mike is 14 year old boy who builds a robot. The robot can speak and is made of wood. They become friends and go on adventures. Create a 1250 word response in the language of English. Response should be written with a flesch-kincaid score grade level of 8.”

Question - What is the proper way to form a prompt generate a response of approximately 1250 words? Is that even possible?