Perhaps a bad example, but how old is the current most coveted striker in Europe?
Age is no boundary if your good enough.
Agree this is what it comes down to. Rooney was starting for Everton at 16, Owen for Liverpool at 18. They were good enough so they played.
Linked to this is what pep has said about how it's very hard in England for a coach to judge whether a player is good enough compared to other countries. In Europe the B teams play at such a higher standard that it's a lot less risky.
"The second teams in Spain, at Barcelona or Real Madrid, play in front of 40,000 people and every weekend in the second league. In Italy or Germany they are so tough, so demanding, they are playing with guys who are 28, 29 or 30 and that is the best way to improve, not training with the first team sometimes."