Most companies in the valley have a terminal level (a level at which you're not expected to progress to the next one) that's close to level 3 in the chart here.

Most companies in the valley have a terminal level (a level at which you're not expected to progress to the next one) that's close to level 3 in the chart here. In my experience, a lot of people don't progress beyond that. For the ones that do, the number of years of experience plays a smaller role than the quality of the experience itself.