FNP -
Based on the convention I was using the chinook age should have been a 4.2 - a fish at the end of its 4th with a freshwater history; my bad -sorry.

I have no idea why a different system is used for chinook than steelhead, unless it is because of both zge zero and yearling smolts chinook are typically found (even some older smolts).

Tight lines
S malma