Well, it is hard to say really because there are so many possible futures in regards to radical life extension. It is likely that if we start to stop the aging process that the ways in which we do this will fundamentally change the human form. As a result, it is hard to say how maturity will change, but generally I believe that as we continue to evolve in new ways with technology that we will become far more intelligent - which is often culturally associated with higher maturity. Intelligence is plastic and always changing. Our brains are dynamic distributed systems that require complex environments for stimulation. Our brains will always be emergent and always changing. What we will need to do is figure out how our brains degenerate over time and figure out how we can stop this or change this from happening while still keeping "you" "you".If we were to stop the aging process, how do you think maturity would be affected, if at all?
Also, is it likely that stopping the aging process would preserve neural plasticity?