If we made sure Einstein's mind never lost its youthfulness, why would we need a next generation? Imagine the outcomes if any of the well-known, world-renowned geniuses got basically infinite time to pursue any projects of their choosing. To think of new ideas, build atop what they've already discovered. Hell, think of everyone else - one could study or research for decades, with professionals in their fields joining forces with anyone who studied enough to join with them. Needing a constant flow of new generations for new innovations seems like a self-imposed limitation, not an actual necessity.
