A senior to me is someone who can tackle complex problems without significant supervision , differentiated from a lead in that they still need guidance on what the overall tasks are. They should be familiar enough with their tech stacks that I can send them to meetings (after the requisite on-boarding time) to represent the team if needed (though I try and not overload my engineers with meetings) and answer feasibility questions for our projects. They don’t need constant check ins on their work. I should be able to bounce ideas of them readily on how to approach bigger problems.

A junior being someone who needs more granular direction or guidance. I’d only send them to meetings paired with a senior. They need close to daily check ins on their work. I include them in all the same things the seniors do for exposure, but do not expect the same level of technical strength at this time in their careers.

I try not to focus on years of experience necessarily, partly because I was supervising teams at large companies very early in my career.