Basically you are competing against the best of your age group in Spain,while half of those you are facing aren't gonna end as professional footballer.
+1
This is one thing which fans often don't get and they are surprised why some players dominated as kid and turned into average players later.
People usually go and blame a coach (Lucho, EV etc) for "ruining" a player.
The thing is, if you play at Barca's youth teams and you are born, in let's say 2004', then you are competing MOSTLY with:
1. kids born ONLY in 2004 and younger
2. plus only with kids born in 2004 who play in Spanish youth teams
If that kid will be the best young player from guys born in 2004 in Spain, that still doesn't mean THAT much, because when he'll turn 18 or 20, he WON'T play anymore ONLY with guys from his age group (2004) but with guys who were equally as him:
1. the best in 2003' group 1 season before his success
2. the best in 2002' group
3. the best in 2001' group
4. the best in every group from 2000 to 1990 or 1985
So, if some Alena or Oriol is the best player in his age group, then in the next season, he will play at Barca with Alenas and Oriols from 2000, 1999, 1998, 1997, 1996, 1995, 1994, 1993, 1992, 1991, 1990, 1989, 1988 etc.
What is worse, a club will buy 10 other Alenas and Oriols from France, Brasil, Netherlands, who were the best in their youth leagues also.
So, in youth teams:
1. players play only with guys from their age group
2. and only with players from their country (in their age group)
While when they turn into seniors:
1. they play with the best players from 15 different age groups
2. they play against best players from 50-100 different countries, not only from Spain
So, an analogy would be:
1. when you play in youth teams, that is like being the best in your high school between 20-30 guys from your school
2. when you turn into seniors, you as the best guy from your high school, now have to compete with 1000 other guys who were the best in their 1000 high schools, plus you have to compete with 1000 best guys from different high schools from generations 2002, 2001, 2000, 1999, 1998, 1997, 1996, 1995, 1994, 1993, 1992, 1991, 1990 etc.
My post will sound negative again, but please, don't hold your breath too much just because someone is good when playing against other 13 year old kids.
When he'll become a senior, he will never again have it "that easy" that he will be allowed to play only against such a small sample of players.