(Egan is five months old, so, let me do math here.
America is 241 years old and is in his twenties.
That could give me a rough image that nations age one year for every ten, then stop at a given point.
This would mean that they age one year every 3,650 days.
In five months, they would be at 22.967... Percent.
If you plug this back into the time scale, this would make them around eight years old by rounding.
(This is all geometry has taught me. Finding the age ratio of fictional characters