Sounds like oil could be leaking into the sparkplug tubes while sitting and when it's started it burns that oil off. If this is the case...should be an easy/cheap fix. Not necessarily a sign of high mileage.
On a side note...even if an engine has low mileage, that doesnt mean that it was cared for properly by the previous owner.
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1993 Camry LE I4 Bone Stock - 380,000 miles (as of Aug '11)
1993 Camry XLE V6 Bone Stock - 260,xxx miles (as of July '11) Blown Head Gasket
2003 Chevy Trailblazer EXT I6 - 107,000 miles (as of Aug '11)