Why do so many people die on their 21st birthday?
They say, "Hey, look at me, I can drink alcohol" and decide to drink a crap ton. You don't even need to do something stupid while drunk, you can just as easily drink so much that your body can't cope.
Because they can drink alcohol
Possibly from alcohol poisoning,drunk driving accidents, or other alcohol related incidents since you can LEGALLY drink on your 21st birthday.
Maybe because they have cancer