The world class players of yesteryear were almost certainly created on the streets of Glasgow, Edinburgh, Aberdeen etc. - just like the England '66 world cup winning team. You get a similar thing with players that came through from playing cage football in various places. To be really good you need to be technical, physical and have a few tricks up your sleeve. But kids today can't play in the street and there aren't enough cages etc. available, so it's in the playground for half an hour at school and then local club training. That makes it absolutely critical to have top class coaching and a footballing development philosophy that emphasises technique over strength/speed.
I can't remember where it was, but someone did a study that showed that professional footballers skewed very much towards people that were the eldest in their cohorts growing up - it was dramatic. In the UK, a September kid is far more likely to be successful than a May kid. This is despite the fact they'll end up the same size as adults. Any decent coaching system should work to try and remove this bias - by focussing on the technical aspects and giving kids space to develop, rather than cynically selecting on performance alone each intake. That also means not focussing on winning matches in youth football, but on developing players. A lot of budding Guardiolas and Fergussons don't like it, they treat every game like the Champions League final.
Sorry, on a rant again, it still smarts all this time later. A succession of coaches failed to noticed my lad could take a high ball down with the outside of his boot and turn on it with a defender up his arse, or that he looked to bring his teammates into the game, but did notice he didn't shoot powerfully and could get kicked off the ball. The one time the coaches did notice him was when he was pissed off with the ref, the opposition, his teammates and his coach and got the red mist. He just ran through an entire team to score. Coach thought he'd turned into Maradona. None of them worked out how to get the best out of him, and most overlooked him for more physical and aggressive players. I'm not saying he was the reincarnation of Michael Laudrup, but because he didn't put himself about he just wasn't on the radar. The qualities he had just weren't prized.