At what point does a footballer...

At no point. Players are different. One player might have reached his potential at twenty-two, another at twenty-eight. This is especially true for certain positions. For pacey strikers, it seems they reach their potential much earlier, than for example, central defenders.

So the point the player goes from being a hot prospect, is basically when he is an important member of the squad and isn't just trying to become one, in my opinion.

when liverpool buy them.

when liverpool buy them.
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Gotta laugh at that one.

TOOR-Agree with you there