One of Heinlein's books plays with this concept. There's a Martian race that are essentially immortal, at least from natural causes. Every 40-50 years they go t

One of Heinlein's books plays with this concept. There'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's explained that it's how they are able to rejuvenate themselves.