In Germany, players are considered young up until 23. Years back in England, you rarely got a chance in the first team till you were 20-21. It's only in the last 10 years that we've felt a need to rush players through.
Hopefully this will work out well for us...but I can't honestly remember a player who was let go from an academy at 16-17, who then went on to be a star in the Prem.
Having said that Lallana didn't really start to show his true potential till he was 19-20.