Age doesn't matter. The title exists if someone else thinks your senior in the context of your current work. Senior at company A may be Software Engineer II at

Age doesn't matter. The title exists if someone else thinks your senior in the context of your current work. Senior at company A may be Software Engineer II at another due to organizational differences or lack of experience in the topics worked on. From my limited experience, a senior engineer in my eyes is someone at work who is a subject matter expert in the systems they are currently working on within their team or department. In addition to that, the litmus test I use to classify a senior engineer is, "would I go to this person for advice for most issues or questions I have within this team?" For me it's both technical expertise and sophisticated communication skills to be able to effectively communicate to other team members and mentor them. Beyond this role, I see ownership and autonomy within larger parts of system as being the next step.