Hyphenated ages

[Foolacious]

Has hyphenation of ages become the standard in all grammatical contexts?

When I was in school (60's and 70's), here is how ages were presented:

Rover is a 12-year-old dog.
Rover is 12 years old.

In other words, if the age functioned as an adjective, it was hyphenated; as a copulative predicate, it was not.

Now I seldom see, even in formal publications, the non-hyphenated form. Instead, it's:

Rover is a 12-year-old dog.
Rover is 12-years-old.

Oddly, I only rarely see this form extended to other measurements, like height or time.

Rover is a 30-centimeter-tall dog.
Rover is 30 centimeters tall.
RARELY: Rover is 30-centimeters-tall.

It was a 100-year war.
The war lasted 100 years.
RARELY: The war lasted 100-years.

Anyone have a copy of Chicago Manual of Style or other authoritative source handy?