The most common measure used to tell the level of seniority of a developer is years of experience.
I couldn’t disagree more.
If you are working on the same project, with the same technologies for the last 6 years, chances are you pale when compared to another developer with 3 years of experience and two or three different projects under his belt.
Experience is the keyword here.
The more diverse the environment, the more you learn, the more you grow.
But what if you can’t just pick your projects?
The best way to level up is by trying new things on the side.
Pick up a new project that interests you and experiment techniques, tech stacks, concepts and whatever comes to mind.
Pet projects allow you to use all sorts of things that may rarely come up in a client’s project in your day job.
Deliberate practice is the most important aspect of growth, either on the job or just for fun and curiosity.
But not just any practice, for further reading on the learning topic, I have this other post Machine Learning for Humans: how to learn better and faster?