your colt huntsman was made in 1975.
It would be 55 years old, made in 1956.
It would be 53 years old, made in 1958.
your colt huntsman was made in 1974.
It would be 55 years old having been produced in the first week or two of 1955. Proofhouse.com shows that the year 1955 started with serial number 90001-C