You have a pattern of double adjectives - nothing wrong with that, but when it's several times on the same line, it's a problem. A problem of rhythm, which affects how good it sounds to the ear. The word choice themselves are good, I think. The adjective clusters: "jet black, short and slick; three-day stubble hid a handsome, rugged face; wicked, childish smile; fierce coal-black eyes... from narrow sockets". It's way too much - space them out. Also, "narrow sockets"? Even in context, my mind jumped immediately to electric sockets. It's just awkward, imo. I agree with another poster re the line "His age was hard to place" - perhaps in context, it's clear it's Freddie who saw knowing in the guy's eyes though. It may be fine depending on how it sits on the full page. However, that line in general is hard to read, regardless of POV - it's clunky. I'd rephrase. Grammatically, I'd argue "Cooper nodded slowly" should be a new paragraph, as it's not Freddie anymore, who begun the paragraph. Also, now I'm confused who the "young man" was - why is he being described this way if the POV was Cooper's and he's describing Freddie? Unless Freddie was a stranger, no one's gonna give that sort of description. I think you have some dissonance there between character POV and your need for description. But again, maybe this is because these paragraphs have been taken out of context - you'll have to inspect it as a whole scene to really know, I think. In any case, who the hell cares what a computer programme says? Writing isn't Maths. A computer can't tell you how good your writing is. If you believe its verdict on sticky writing is valid, by all means make changes. But if you disagree, then ignore the computer. You're not writing to pass a test mate lol. The writing reads well - just need some minor edits, in my opinion.