Bones will stop growing lengthwise between 16 to 18, but you'd want to wait a year or so to be sure.
It's bone density that continues until the mid to late twenties.
So the organisation that made Laura would probably be at least 19 before they added any adamantium to the rest of her skeleton. If they were ever going to do so.
There are some drawbacks to a full skeleton coated with adamantium.
- Its heavy. Logan weighs 300lbs, about 136kg. 100lbs (45kg) of that is the adamantium in him. That throws off a lot of ways Laura could be sent on missions, or extracted, if she were still an assassin. They got what they wanted coated.
- It makes Laura more dangerous, but would also prevent her from being tortured by the people who made her and trained her. One of her instructors, Kimura, chopped off an arm with a chainsaw. Because she could. Couldn't do that if Laura had a fulled coated skeleton.
- It's expensive. Prohibitively so. The existence of her "sisters" in 616 showed that Laura was meant to be the blueprint for assassins. Its easier and cheaper to coat the claws than the entire skeleton. Imagine the dozens of times over. Or just take that 100lbs of adamantium and see how far you can go just coating 6 claws.