This features helps you to find how many days old are you. If the year is not provided by default Alexa will consider the current or future year.
You can also try the following
Sample: User: Alexa, lauch the days I lived on earth Alexa: Rait for response from alexa. User: Examples: 1. How many days I spent on earth 2. Just say your date of birth in the format "21st April 1993"