"hundreds of years" or "hundred years"

Question

Second to KL in size are the historic trading cities of Melaka and Penang, with buildings dating back hundreds of years.

If I wan to say the age of buildings in Melaka and Penang,

1.Buildings in Melaka and Penang are hundreds of years old.

2.Buildings in Melaka and Penang are hundred years old.

I want to know whether "hundreds of years" and "hundred years" are the same in meaning.

Answer 1

hundreds of years old

This means the exact age is not known. But it is in the order of hundreds of years. It can be one hundred, or many hundreds, for all I care.

hundred years old

This means that the age is exactly 100 years. Note that it is a subset of the other one.

Clearly, both of these have different meanings.