An Identification Card is a document that proves a person's identity. Various personal information is included in an ID card, such as your full name, date of birth, age, address, citizenship, profession, religion, and an identification number. ID cards in the United States are issued by the Department of Motor Vehicles (DMV), which is a state-level agency.
In the U.S., driver's licenses are considered a replacement for ID cards, and can be used as an identification proof for various purposes, apart from it's primary purpose, which is operating a motor vehicle. People can buy alcohol or open bank accounts using their driver's licenses, without having to apply for an ID card.
But, if you don't meet the age requirements for a driver's license, or you simply don't own a car and you don't intend to drive, so there is no need to apply for a license, having a photo ID is somewhat of a necessity. Without it, you can't even get a job, get on an airplane, or buy cigarettes.
When it comes to applying for an ID card, there are certain requirements that you have to meet, but there are no age limitations, as with a driver's license. Everyone can apply for an ID card, no matter how old they are. Some states issue ID cards that are only valid for a couple of years and have to be renewed after a certain period of time, while others issue ID cards that are valid for life.
You have to visit your local DMV office to apply for an ID card, and you can make an appointment beforehand for faster service. You have to provide your Social Security Number, and complete an application form. Then, give a thumb print, have your photograph taken, and pay the required fee, which varies from state to state, but it's usually about $20-30.