how does ageing work? what are the differences between different kinds of alcohol?

i have a fantasy character that has a very long lifespan (like how some crustaceans are technically immortal) and thought it’d be a fun idea to have her run a business selling alcohol she made long ago, but i don’t know how ageing works, what types of environments are secure for barrels to age, if there are significant differences between types, and i would like to hear about the process since it sounds interesting. i’ll ask my dad, who used to have a hobby of making mead, but i enjoy getting info from as many sources as possible.