I don't think you pay that much for a 24 year old and don't immediately have them in the starting line-up.

Cazorla was a winger who became a CAM when he lost a bit of his pace. Eventually he transitioned to a CM role in his late 20s (maybe even early 30s, I can't remember). Late 20s is when you can expect attackers to sometimes be able to adapt to a defensive role. Wingers switch to fullbacks, CAMs become CMs, etc. By that time they have enough experience to read the defensive side of the game well, and know their positioning.

But, even with Cazorla, he was at his best when he was paired with a very defensive player. His best year he was next to Coquelin who was basically nothing but a midfield destroyer.