Tarrant is already 30+.
Warnock is 26, a grade below but will cover the spot whilst you develope a kid.
Tarrant is 29, Warnock 26, and is twice the player Warnock is and Carlton would feel having made the finals 2 years running that they could challenge for a premiership if a couple of things fall into place, like another key position defender and a key position forward.
Carlton should be in a position to be looking for immediate results.