Would they ask for ID if you buy cigarettes?

Yes. In the US, most states have a requirement that anyone selling or distributing tobacco products must ask for proof of age if someone looks like they are under a certain age. For example, in Tennessee, they have to ask for an ID if you look like you are under the age of 27. In some states it is under the age of 35.

Please note that an employee can lose their job if they sell cigarettes to someone who is underage and a business can be fined if they sell cigarettes to underage people.