Yeah but isn't AKC full height at 15? Not sure I agree with that but for many smaller dogs it's probably okay.
I would say then NADAC should consider 12 for this then, since it's all flat anyway.
I still say a dog who cannot run around an agility ring (which is a good appropriate running surface!) for a minute or two by a *year old* is not sound enough to do agility at all. No directed running before 18 months means "dont go leash them up and for a run with your dog" not "your dog shouldn't run". Because Joe Public gets a puppy, they're energetic, person likes to jog/run, so leashes up their puppy and goes for a mile or more run. That's not safe. That's what people mean when 'dont run with your pup!" is said.
Teaching a pup to go around a cone (which they will probably run to do!), or letting them romp in the yard, or meandering hikes on natural surfaces, restrained/runaway recall training, flatwork 'shadow handling', etc, is all good! Uses their brains and teaches them about sticking around off leash, recall, following directions. There is safety, and then there is tying their legs together and wrapping them in bubble wrap.

People getting a puppy for agility are not going to be in the Joe Public group. And if they are, they may find agility around 6-8 months when their pup is now adult sized and still "crazy!" without a job or any training; and they'll be going to a *trainer* for those problems and get into agility that way.