With this vintage table you can see which years were good and which years can better be avoided for the purchase of a Chianti or Chianti Classico. Of course this list does not guarantee a good Chianti wine, there are more factors involved such as the winery and even the specific vineyard of the winery from which the specific bottle came from.
Chianti wines cannot age very long, most of them you should drink within 3 years when the wine is still young. Chianti Classico can be kept for a bit longer, but not much longer than 5 years.