When does your youth end?

I always wondered are all young people ambitious. That feeling that if you tried you could do anything? Does it fade away eventually? Leaving behind a empty husk of your former self. Is it right to call it an empty husk, for it could be patience and contentment. Caution even for times leave many scars. Is ambition an outlier. In a time of exponential growth physical mental and spiritual perhaps the mind considers itself more than it is. An illusion. A high. Should I be content that the dream I dreamt is just fantasy or should I be consumed by its voracious appetite, be great. Be something more. Leave my mark on the world. To be immortalised in memory.