"lee martin and spector ive neva seen 2 b honest so i cant comment (ive neva seen them play 4 england side tho so i doubt they can b that gr8)"
First of all, Spector is American so that would make it really hard for him to play for England, eh? He was the best defender on the USA U17 national team with Freddy Adu at the World Youth Championships, voted one of the best defenders of the tournament, and from what I've heard first-hand from people who've played against him, he has as bright a future as any young defender. Top class potential.
Secondly, some players develop much later than you'd think. Dado Prso was still playing Sunday league in Croatia at the age of 22. Seven years later he was lighting up the Champion's League and widely considered Croatia's best player. Not every world class player was a superstar teen, and not every superstar teen becomes a world class player.
The reason clubs like Man U, Arsenal, and Chelsea buy these teenagers is because if just one out of 10 or so live up to their full potential, they'll easily make all their money back. The odds of one particular player becoming a world star are still very very low. Often the best players come almost from out of nowhere (Zidane, Deco, Maniche, Costinha, Carvalho, half the rest of the Porto squad, Henry to some extent).