A quick track from juniors to experts is to convince someone to let you build something big from scratch. It is going to be messy and likely difficult to maint

A quick track from juniors to experts is to convince someone to let you build something big from scratch. It is going to be messy and likely difficult to maintain. But you gain immense experience from that project, so much that you can be a semi expert (and an expert in that specific domain) in just a couple of years. That was how tons of young people who trampolined to senior in just a few years, bagging a lot of experience in the CVs.