Where I live you honestly can't say that diet stunts people's growth. That would apply in places where food isn't readily available, but certainly not in the western world. From looking at people I know I can tell you too, that the differences in muscle size is more related to how much muscle they had before going to the gym than how much time they spend there.
Can you start going to the gym and get stronger than your friends who don't go? No. Out of 10 friends maybe you'll pass 1 or 2 of them in strength, but that's it. That is what I have seen but I'd say it is pretty far from what you suggest.
Can you start going to the gym and get stronger than your friends who don't go? No.
Presumably your circle of friends consists of people who are already physically active. Even so, I doubt your assessment concerning strength training. Looking at the people around me, I'm guessing fewer than 5% (not 80%) of them are up to 100 pushups [http://www.hundredpushups.com/]
You presume a) everyone has access to healthy food as kids, and b) strength training is nearly ineffective.
What, you forgot about the massive population of poor the world has, western included? Or how many in the western world eat crap, because it's easier than making things for ourselves? Height is largely determined by what your parents feed you, once you're able to be on your own you're essentially fully grown. I know a decent number of people whose parents were either relatively poor, and they subsisted on mac & cheese frequently, or were largely idiots when it came to food and raising kids. And many of them are noticeably shorter than average. My wife, for instance, is just barely over 5 feet, and her family-then-single-father fell into both categories until he joined the military.
As to the second... I have absolutely no idea where you get that idea from. Maybe everyone around you weight-trains outside of the gym frequently, or you've never done so for an extended period of time? You're absolutely nuts, though.
It wasn't about me, I've been doing sports my whole life but never tried weight lifting. Before I spend my time writing a reply, please answer this question. Do you think that if we all lived in the same environment, had the same diet, did as much physical exercise and all other variables were the same except our genes, we wouldn't see a difference of 1 foot between people or a difference of pounds of muscle mass? And more related to the article, we wouldn't see a difference in intelligence?
Foot between heights: assuming identical diets, absolutely. Different people metabolize and absorb things differently. Assuming ideal diets for everyone, I'd bet a foot would be near the limits.
Muscle mass, depends significantly on how much exercise. Some respond to it differently than others, so some would be more muscular with light exercise while others would be more with heavier. A difference though, yes; if somewhere near the middle, accounting for height / overall body build, a moderate amount of difference, but not a whole lot.
Intelligence, barring physical defects, I don't know. People certainly seem to have specialties, especially if you consider some of the "greats" of history as nigh-savants, but measuring an overall intelligence of a person is a nightmarishly subjective task. Very broad statement: not much of a difference. A lot of specialists are severely lacking in communication skills, a lot of artists in engineering, etc, and those deficiencies would have to be factored in.
At the end of the day, I'd bet we're all pretty darn similar. But I do lean significantly towards the nurture-over-nature side of the argument; do nothing, and you become a blob, regardless of your biology. It happens to animals too. There are, of course, some differences, but you have an incredible amount of control over what you make of you.
Can you start going to the gym and get stronger than your friends who don't go? No. Out of 10 friends maybe you'll pass 1 or 2 of them in strength, but that's it. That is what I have seen but I'd say it is pretty far from what you suggest.