.... more then likely he is sensitive to extract twang.....
This.... All the other suggestions - Water - Fermentation control - yeast - all right on the money but I read through this whole thread and only saw this mentioned once.
Some people, myself included can just taste that "extract twang" ...and I'm not saying you can't make good beer using extract, I have and did for years - like since the early 90s, but it always had a taste in there that I didn't like. Sometimes very faint (fresh LME??) Other people raved about my beer and came back for more...but to me something was off. It was good, but not commercial beer good.
When I finally went AG - BIAB - I could not believe the difference and I would have argued there would be little difference. Since going AG I haven't had a bad beer...well other than one or two that my choices of hops just didn't quite play well with each other, but the beer was good!
My 2 cents!
Cheers! Don