It has more or less been at least conceptually proven[0].But I think many people confuse a well-organized mind: which can function well[i.e take better shortcuts] at an old age (and thus give you the impression that the mind is still very fast) with neuroplasticity.This is not necessarily the case, and not necessarily even better, think something like overfitting.Then again without defining speed and time(which are hard to do not understanding the mechanisms of consciousness,if possible at all) the discussions are kind of up in the air.I wonder how much the emotions play a role here, because anecdotally being emotionally engaged can 'slow' time down for a person. [0] https://www.cambridge.org/core/services/aop-cambridge-core/c...