It's in the PSA that you're required to read - http://www.cj.com/psa.html - search for "years". You must be 18.
You have to be at least 18 to make sure you can accept your payment, but some publisher under 18 still apply with their parent name and bank account.
Hi, I presume you should be 18 years and above. But I would request you to go thru the publisher guidelines for exact clarifications.