I got my PS3 account when I was 12 years old, so I was unable to have Facebook on my account. But now I'm 13, and I still can't get Facebook on my account.
It's not an age restriction. It's an account type restriction. PSN sub-accounts don't support Facebook integration for legal reasons. As long as you are a minor, you are only permitted to use a sub-account; so you won't be able to use Facebook integration. Your current PSN account will always be a sub-account, so it will never be able to use Facebook integration; no matter how old you are.