You can add muscle naturally. Who is disputing that? Adding any appreciable muscle while doing massive amounts of cardio like boxing is nearly impossible, at any age.
thats probably why he gasses against 40somethings. That is kinda an pretty majorly embarrassing statement, when you look at it.
this is a really good point. It's very hard to gain muscle during a typical training camp cycle (8 - 12 week). For someone over 120 kg, for instance, to consume the necessary amounts of carbohydrates (for energy) and protein (for muscle mass) would require an eating schedule that would conflict with training. what's more, during an ordinary camp cycle, sparring and heavy bag sessions (among others) are frequent enough to prevent muscle tissue damaged during lifting, to properly recover.