If someone proves that players lose their eliteness at 30, I will not discuss the Sox getting Mauer ever again. A player's prime is usually between ages 27-32, this basically kills that theory. Considering that Mauer isn't a power hitter, the skill that diminishes first, I'm not worried about him declining.
He has a sweet, smooth swing, and I could see him hitting over .300 well into his 30s. Comparing a player to a position is absolutely foolish, you compare to skill sets. Mauer's skill set translates well going forward IMO.