I think it takes the USA about 6 years, start-to-finish, to create one of our latest Nimitz Class carriers.
The Chinese are having to start from scratch. The US, on the other hand, has all the infrastructure, designs, workforce, experience, etc. in place to allow for rapid construction of the aircraft carriers.
Also, the Nimitz have been around since the late 60's. And have had 40 years of improvements, design changes, etc. since. And a host of lessons learned since.
So, the biggest limitation in the US of doubling or even tripling America's aircraft carrier force is medicare, medicaid, and social security :)
And while welfare programs hurt as well, the big three are in fact the gorilla in the room.