Idle musing led me to realise that in some of the languages I know I am much younger than my physical age, having learned them at different times.
In English, for example, I am long in the tooth. In French and Spanish, I am much younger.
Presumably, were I to learn another language now (which one would it be?), I would be really, really young.
I suppose this means that if you want to stay young (at least in spirit), you should learn a language.