OZONE [not platypus]Long in the tooth
OLD [what you'd have to be to remember that expression]Nipper's co.
RCA [definitely not a puppy]6-Across suffix
ISM [opportune placement] Two foursomes
for OCTET suggests that the latter is composed of two groups of four, but an octet is not by definition divided by sub-groups. Similarly, four duos or eight solos do not comprise an octet.
For TILTS replace Pinball no-nos
with What a romantic does at windmills
For TARP replace Ball field protector
with Baseball cover