I think Taylor was cast well as young Jacob because in the first book isn't he supposed to be 14 to Bella's age 16? He looks young, and should appear younger looking then Bella until he shifts then I think he matures to at least looking the same age as Bella or maybe even older looking. But, he is still technically two years younger then Bella.
I would hope that they would use younger looking Jacob until he changes and then replace him with the older Jacob for remaining movies.
I agree with oneTVslave I love Eddie Spears because he looks as if he belongs in LaPush! Taylor has the Indian high cheekbones but Eddie looks great! IMO