In the first example above, old is a perceived quality, and therefore gradable, in the second old has an absolute value, with the meaning of former or previous.
See gradation and comparison of adjectives below.
Use of adjectives
Adjectives are used in two main ways; they can either be attributive or they can be predicative.
Attributive adjectives :
This is the most common use of adjectives, standing next to a noun in a noun phrase. In English, simple and complex adjectives almost always come before the noun . Examples: The big metal box My dear old grandfather . A very modern plastic dish. An easily recognisable face. A pink and green dress A not-too-infrequent event.
There are only a very small number of exceptions, notably concerned involved, present and responsible, which have a particular meaning when they come after a noun. There are also some cases in which old and tall follow the noun The other important case when an adjective will follow a noun is when the adjective is postmodified by a prepositional phrase. Examples: All the people concerned were