It takes about 1 yr for the phone to be eligible for unlocking. So all the iPhone 6 and 6+ should be able to unlock now. But 6s and 6s+ will not be unlockable yet. You can try a 3rd party site if you need them unlocked.
What do you mean when you say that it takes about 1 year for the phone to be eligible? According to AT&T, eligibility requires that "all the device’s service commitments and installment plans are completed, and all early termination fees are paid in full." That depends on the plan you're on. For example, my Next 12 plan is up in September. Every time I've submitted an unlock request online, I've received a response almost immediately saying that my phone isn't eligible.
I believe that some people are getting AT&T to unlock phones that aren't supposed to be eligible according to AT&T's own rules, but I don't understand what they're doing differently.