What type do you have that laid at 16-weeks?
Whaat
In ten years I had two different pullets that laid their first egg at 16 weeks. They were not a breed, One was a mix of hatchery birds, Speckled Sussex, Black Astralorp, Delaware, and Buff Orpington. I don't know how much of those breeds was included in that specific pullet.
The other pullet was a mix of those plus some Black Ameraucana I got from a breeder and hatchery Buff Rock. Again, not sure what percentages of any of these breeds.
If I hatch ten pullets from my flock I normally expect the first egg around 20 weeks with most of them laying within the next two months. Sometimes mot of them start closer to 20 weeks, sometimes closer to the 28 weeks. Each year it varies. I got the same spread with the pullets I got from hatcheries when they were a breed before I mixed them. A few of those started at 17 weeks.
People want to think that a certain breed pullet will start to lay at a certain age, no matter which hatchery or breeder she is from. Real life doesn't work that way.