All of Smule's apps (Smule, Autorap, Magic Piano) are free apps and can be downloaded by anyone. Due to safety measurements, the Smule apps can be used by users that are at least 13 years old if they reside in the United States and at least 16 years old if they reside in the European Economic Area. If there are users under that same age it is mandatory that they have Parental Consent.
You can find more information here in our Terms of Services: https://www.smule.com/en/termsofservice