I don't think Milton wrote An Extempore Upon A Faggot. It's tone (clever adolescent poses as man of the world) is wrong- not just for him, but for his period. It feels very post 1660 to me. Besides, I understand a version of it turns up in Rochester's Collected Works. My guess is it belongs to neither of them- and its attribution to Milton (in an obscure Miscellany) is simply a sly, early 18th century joke.