A whiskey’s age statement refers to the time the whiskey has spent aging in a wooden barrel. It specifically refers to the youngest whiskey in the mix.
Older whiskeys are typically mellow and more expensive. You'll also see many bottles with no age statement at all, including many reputable entry-level whiskey brands.
Whiskey mash is the mixture of crushed grains and water that is cooked together to convert the grain's starches into sugars, which ferment and form the whiskey base.
The term "mash bill" simply refers to the grain contents of the mash. Since each grain lends its own flavor and character to the finished whiskey, this is important information.
Peat is compressed, partly decomposed plant matter historically used to heat and dry germinated barley. Peated whiskey has a more smoky quality than whiskey made with coal.