In the book I mentioned earlier, Gladwell talks about how the better Canadian hockey players tended to be the ones born in the early months of the year (e.g. Jan and Feb). It's because the players are grouped by their birth year, and selected when they are 8-year-old. At that age, a year difference in age between a boy born in January vs. another born in December is huge. The older and stronger boys are favored, get more practice, and they keep getting better.
Someone else later found that if a December boy was good enough to survive competition, at an older age he was likely to perform better than the older boy because his youth now became an advantage in adulthood, plus he was likely to be more skillful.
An earlier poster mentioned that CEOs tend to be men of better than average height.
Some of these effects are clearly observable and have a logical cause. But life is often unfair like this. You just have to find a way to compensate for your disadvantage.
I was more successful in school than my two younger brothers. I had higher grades, spent much less time in college than they did, and generally sailed through school. But later in life, I got bored at my megacorp and left at the age of 40 to pursue my own dreams, which crashed and burned (I was not as good or smart as I thought). My brothers stuck with their own megacorps, and toughed it out. We do not share net worth numbers, but they are doing well financially.
If you are not pretty, it is not easy to become a model. If you are not big and tall, do not try to be a sports player. Life is not fair. What else can you do, but to work with what you have? You will not be a billionaire, but you can be financially secure. One should not waste too much time to complain.