I would guess ca. 1990 from the fork design. OS refers to "OverSize tubing," which became popular first on mountain bikes and aluminum frames. You may be able to decode the date of manufacture from the serial number; whereas the Varsinentals went to a 2-initial-letter serial number scheme in 1965, the Paramounts, KOMs, etc. retained the original single-letter code, in which the initial letter denotes the month (skip I, so J=September and M=December) and the digit immediately following it is the last digit of the year of manufacture. The headbadge may also have a 4-digit code, in which the first 3 digits are the day of the year (1-365) and the last is, again, the last digit of the year.