i personally consider a players 'peak' 26-28 years of age, except for 'star' players, so, getting a guy at 25 would be just before breakout, but, these are all short term deals, so, if they do breakout, all they become is decent trade chips, or too expensive to resign.
to gamble and win, you need to sign the 25 year old, on the verge of a breakout to a long term deal on the cheap.
i.e. if Bunting was signed for 5+ years at his cap hit, then he'd be a steal if he improved, while still manageable if he doesnt.