Medically, youth has a particular meaning related to time of life. We cannot blink that away.
The average youth has vigour, speed of reaction, resilience, and healthy state of organs in comparison with even a fit person who is older.
The average young person doesn't have wrinkles, or drooping bits.
But a person in what's called middle age might be more attractive and/or healthier than someone younger. Many faces seem to have a blandness in their teens or even early twenties, and only develop a more striking appearance somewhat later on.
If what's meant is more about a youthful outlook, that may have more to do with life experiences, past injuries, past traumas, past achievements, training, confidence... I applaud the emotional outlook that is youthful without being infantile or reckless.
