| | well as i usally say age is the key. buy a preowned saxophone 10 to 40 tears old. dont get it to old saxophones don last for a verry long time. get one that is 100 to 1500. | 
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I agree.  Any sax older than 1500 years probably won't work too well. 
 
 
Seriously though, any well-made sax can last a long, long time provided it is well maintained.  Mine are all in the 40 to 90 year-old range.  So, in reality, age has nothing to do with it.  The condition of the instrument is what's important.
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Oh yeah, regarding the original question about dark vs. bright tone, different saxes will have different sounds, but the mouthpiece has as much or more influence on the tone.  If you want a darker sound for classical playing, try a Selmer Larry Teal mouthpiece and see if that's more the sound you are looking for.