youthfulness

n.

青年，少壮；青春；

1. It is the Foundation of Youthfulness.
   那是年轻的秘诀。
2. But of course we're actually about extending or restoring physical and mental youthfulness and vitality.
   但是，我们当然实际上是扩展和保持体力的和精神的年轻和活力。

Youthfulness and agelessness: a comment
ON THE YOUTHFULNESS OF YOUTH CULTURES
Youthfulness and fitness—Identity ideals for all ages?
Muslim Youth and the Claim of Youthfulness
The inevitable youthfulness of known high-redshift radio galaxies
Youthfulness Responsibility and Punishment: Admonishing Adolescents in Criminal Court
Youthfulness, inexperience, and sleep loss: the problems young drivers face and those they pose for us
Identification of Genes Promoting Skin Youthfulness by Genome-Wide Association Study
Juventude: etapa da vida ou estilo de vida? Youthfulness: a stage of life or a way of life?
Concertina effect and facial aging: nonlinear aspects of youthfulness and skeletal remodeling, and why, perhaps, infants have jowls