Definition - What does Peak mean?
Describing the "peak" of a wine can be very subjective. In basic terms, however, the peak is the age of a wine when it is at the best time in its life. This is when the bouquet, aromas, flavors, complexity and finish are at their best. This is when each aspect of the wine compliments and is in harmony with one another.
WineFrog explains Peak
As wine ages in the bottle, there is a certain "time" in its life when it is in an ideal state to consume and fully appreciate. When a well-made wine is aged in the best conditions with proper humidity and temperature, it improves over time. The speed at which it improves depends often on the blend, the varietal, alcohol, sugar and/or acidity content and the conditions during the growing season of its particular vintage.
At some point a wine will reach its optimum level or best time in which it will not improve any more. This is referred to the "peak". For some time (a limited time), most wines will plateau at their peak, but then eventually begin to decline. For some wines, this plateauing may be very limited.