Your question is more specifically about physical beauty and equating it with the vibrancy of youth. The answer to your question about “true beauty” being found only in young people is “no.” On the surface, there may be young people who appear to have good looks and good physical health but this does not equal “true beauty.”
Our present-day culture glorifies young people—celebrities and athletes—who seem to have it all, including beauty. But we’ve all been witness to the misconduct or entitlement demonstrated by those very individuals. This is not authentic. By contrast, true beauty isn’t something superficial; it is something intangible that is communicated from one person to others. This occurs when we contribute something of great value to the world by employing our gifts and talents to render service—this is true beauty, and its manifestation is not restricted to young people but to people of all ages.
And let’s not forget the old adage, “Beauty is in the eye of the beholder.”