What do the VS, VSOP, and XO grades we usually see mean? They are actually the grading of cognac aging time:

1.V.S. or ★★★ (Very Special): at least 2 years
2.V.S.O.P. (Very Superior Old Pale): At least 4 years
3.Napoléon: at least 6 years
4.X.O. (Extra Old): at least 10 years
5.X.X.O. (Extra Extra Old): at least 14 years

The aging time here is the minimum aging time, and the actual aging time of many distilleries will exceed the minimum vintage by a lot.