Malcolm Gladwell showed how small advantages often turn into huge advantages over time in his book "Outliers". I realize its not universally applicable, but his anecdote shows that more things are winner-take-all than you would think.
Brief Summary of His Case Study:
A hugely disproportionate number of Canadian NHL players are born in the first couple months of the year. Someone investigated this, and attributed this to the cutoff date for kids' hockey leagues was January 1st. Note that this is for ~7 year old kids or something. Because kids grow so rapidly, the boys born in January and February had a small but real size and strength advantage over the hockey players born towards the end of the year. This lead to the older players being perceived as superior (because they were), and therefore getting more attention from coaches and more playing time. This in turn made the gap one not just of size, but also skill. These better players eventually went to play on travel teams and play even more hockey with more attention, and got much better. Some of these eventually went to play in the NFL.
One year difference is huge when in that age range.
I went to school when I was 6,5 years old. Everybody else in class was 7 with some months. I was the weakest and could not do anything properly despite the fact that I'm pretty gifted. I could only get good grades for any subjects in the fifth grade. And even now I feel the weakest and the least protected by default. ADHD certainly didn't help too.
So no, being 7 years old and being 7 and 3/4 years does give you a big advantage. The fact that everybody is uniform only magnifies it.
In the workplace everybody have the different age, story and skill set, so this hardly applies. It's no longer a function of two variables monotonous on both of them, but a function on dozen.
And also while small difference give clear boost in competitive environments, it's not so obvious in cooperative environment.
Brief Summary of His Case Study: A hugely disproportionate number of Canadian NHL players are born in the first couple months of the year. Someone investigated this, and attributed this to the cutoff date for kids' hockey leagues was January 1st. Note that this is for ~7 year old kids or something. Because kids grow so rapidly, the boys born in January and February had a small but real size and strength advantage over the hockey players born towards the end of the year. This lead to the older players being perceived as superior (because they were), and therefore getting more attention from coaches and more playing time. This in turn made the gap one not just of size, but also skill. These better players eventually went to play on travel teams and play even more hockey with more attention, and got much better. Some of these eventually went to play in the NFL.