By the time I graduated I had already worked on 3 development teams in fortune 500 companies. As much experience as people who graduated years before me? No. More experience than people my age who were in just about any other discipline than me? Definitely.
Young developer non-professional experience also commonly dwarfs what you'd expect in other industries. Try doing molecular biology at home.
I don't disagree that non-professional experience is valuable and that it certainly depends on the developer. For example, it's incredibly easy to work on open-source projects or have code on github that's in circulation and supported. And when hiring for a team, they're definitely good signs.
My main point was that the developing software on your own is very different from working with teammates and having deadlines and processes, where you're often required to choose the best of a set of bad options rather than having the time to do things right or where you're thrown into a legacy codebase that can't be broken but must be fixed.
Young developer non-professional experience also commonly dwarfs what you'd expect in other industries. Try doing molecular biology at home.