You're talking about hatchery fish.
They are raised to "smolt size", meaning they head for salt water very soon after they're released. So really, the time they spend in the stream is negligible.
Most (say~ 90%) steelhead in these parts come back as "2-salt" fish, meaning about 2 years in the salt-water phase . These are your average ~5-8 pounders. Some stay an extra year (3-salt) and are ~12-15 pounds. Longer than that probably has happened, but not often enough to worry about.
Wild fish have considerably more complex life histories.
Most may be 2 years fresh/2 years salt, but it varies from 1-4 years in fresh to 1-4 years in salt.
If you look at the WDFW stocking reports, note this:
"release year 2018. The majority of the adult returns from these releases are expected during the 2019-2020 winter and 2020 summer seasons."