I was told that the following sentence is incorrect because in order for a comma to come after a prepositional phrase, there needs to be 5 words in the prepositional phrase.
Under the new legislation, a tax credit was given to students under the age of twenty-five and those earning less than the minimum poverty level wage.
Is this true? It seems to make more sense WITH the comma.
I don't know of any 5 word rule. I think it is right with or without the comma.
Just keep in mind with English that the most important comma rule there is goes: IF IN DOUBT LEAVE IT OUT!