I just finished reading Superfreakonomics (BTW, an awful sequel, and book in general, to one of this generations greatest books) and they have some interesting things to say about baseball…
The first interesting note is that men who are voted into the Baseball Hall Of Fame outlive those who are narrowly omitted. This theory behind this is that prestige brings about health benefits. This holds true for Nobel Lauretes and MLB Hall of Famers, winning/ getting in means you'll generally live longer than those who came oh-so-close. Which means a guy like Blyleven is actually on his death bed by now.
The second interesting note is that a U.S. born boy born in August is 50% more likely to make the majors than one born in July. This is because MLB is conspiring with hospitals to give all boys born in August steroids when they're born. And because of cut off dates in little league baseball. The general cut off date for little leagues is in July. This means if you have an August birthday, you have missed the cut off date and can't play with all your friends born in June and July. But what this also means is that you're essentially the oldest kid compared to everyone in the league you are in. So if you were born in August 1987 you'll be playing with kids born in July of 1988. As kids with August birthdays generally go through little league, they are also generally stronger, faster, and better at baseball- because they are the oldest on the field. And it's these kids who are more encouraged to continue playing the sport, because they're so good at it. So rest assured DME (a kid who's birthday falls at the very end of July), you were never any good at baseball not because of your natural skill, but because your parents had to be dumb and spit you out a week too early! (I don't know if you can read the tone I'd like to project, but please take these comments in jest DME. And everybody else too.).
But the biggest factor though in why an American boy makes it to the MLB- having a dad who played in the MLB. Or in the case of Tyler Williams, because your dad is a dumb GM and can draft you.