[mful]

It's hard to imagine you actually believe that maturity and experience are not related to job performance. Regardless, it might be helpful to think about experience as a hiring heuristic, like having a college degree: you certainly don't need it to be a good programmer, but having it is positively correlated with skill (in a way that is rationally causal, unlike, say, race). Recruiting, screening and hiring are massively expensive. Screening every inexperienced candidate who wants a senior position to find the rare gem would have an outsized cost.