One of Heinlein&#x27;s books plays with this concept. There&#x27;s a Martian race that are essentially immortal, at least from natural causes. Every 40-50 years they go through a change and become childlike for 5 years. Lack of awareness, playfulness, no interest in sex, and an emotional state that changes quickly.  It&#x27;s explained that it&#x27;s how they are able to rejuvenate themselves.