In Colorado, it is a state law that you must have your ID on you while possessing alcohol, even unopened, no matter how old you are.
In Michigan, it is a state law that you must have your ID on you at all times, no matter the circumstance.
Many other states have similar laws as well, so technically, even when you're 80, you should still be IDed under most state laws. Most places don't if you're obviously 40 or older, but technically they are supposed to. So, get used to being carded.