The couple of long-term data sets I have seen on steelhead age show a couple of interesting things. The R/S increases as total age of the fish (measured only for first-returning fish) decreases. This fits with the observation that the longer they spend in the ocean, the fewer come back.

Age in steelhead is interesting. It appears that freshwater age is primarily controlled by the environment; higher productivity in the stream produces younger smolts. It also, based on Canadian studies, produces more smolts. This makes a two-edged sword that lowers returns; low FW productivity produces fewer and older smolts.

At the same time, salt-water age appears to be primarily controlled by inheritance. This is why practices like breeding the big Skamania summers with each other led to big fish coming back but fewer fish. As I recall, removing the smaller, younger fish from the broodstock led to a program that wasn't self sustaining. Again, older fish, lower R/S.

The above is applied to first returning fish only.