Why would you change the age for Coppa? COPPA or Child Online Privacy Protection Act. Is made to protect children's privacy online. This is meant at the predefined age. If anything if something happens and you set the age higher, you can have some issues with the ACT
if your going to change the age, you might as well change the contents.
http://www.coppa.org/coppa.htm
if anything you nulled the agreement for coppa. The agreement is built around "Children" under the age of "13"
im not against the idea of changing your minimum age requirements. However you should at least change the coppa agreement to meat the necessary needs for your age limit.
Quoted from
COPPA - Children's Online Privacy Protection Act
"(1) CHILD.—The term "child" means an individual under the age of 13. "
If anything is this a good idea for changing the age limit. but please know that by doing this you null that COPPA agreement. COPPA does not protect users over the age of 13. Therefore you are at risk.