For many companies 'senior' engineer is a terminal level, meaning you can continue on it and will be respected if you do so. As you've said, both Staff or Eng.

For many companies 'senior' engineer is a terminal level, meaning you can continue on it and will be respected if you do so. As you've said, both Staff or Eng. Manager role carry out more responsibility, as they are both leadership positions, one being more technical and the other more related to people. There's a natural push for sending experienced people into the Staff/Manager bracket but I see plenty of people in their 40s and 50s working happily as a Senior Developer.