5. Age
The longer the spirit is stored in a cask the more opportunity that cask has of imparting its flavour to the spirit and the original flavours of the new make spirit become less prominent. The climate in the location a cask is stored also has an impact on how quickly the cask imparts its flavour to the spirit: warmer climates tend to allow spirit to age more quickly. The optimal balance of flavours from the new make spirit and the cask is a matter of taste. Older whiskies aren’t necessarily better, although they are generally more costly as approximately 2% of the spirit evaporates each year from the cask (the ‘angel’s share’) leaving incrementally less of the spirit for bottling.
Bottlings of whiskies (even single malts) can effectively be blends of whiskies from a range of casks that are of various ages. This allows the distillery to have greater control over the consistency of the bottle’s flavour profile. However, none of the spirit in the bottle can be younger than the age statement on a bottle.
No age statement
Bottles containing no age statement on the label can contain a whisky that is as young as three years old, although this can be blended with whisky that is much older. The portion of younger whisky in the final bottle can vary, but typically you can expect to notice flavour derived from the new make spirit. The flavour of new make spirit can vary significantly from distillery to distillery, but expect to notice additional vibrancy or even 'funkiness' to the flavour of the whisky.
Further reading: https://www.whiskyandwisdom.com/young-whisky/
12 years
It can be argued that aged between 10 and 12 years is the optimal age for whisky and it’s not worth paying for the additional cost for older whiskies. Obviously, this is down to personal taste and preference. Expected to notice a broader range of flavours compared with an older whisky.
18 years old
By the time the spirit has aged for 18 years, there is typically very little of the original new make spirit flavour remaining evident in the whisky, having been masked by the flavours imparted by the cask it has been stored in. Expect to notice the deeper flavours of caramel and dried fruits.