If we haven't done, learned or created anything new in recent times, we've stopped being 'young'. I look at guys like 80 year-old visionaire Loren Cunningham of Youth With A Mission, and to me, he gives off the vibes of an idealistic 20-30 year old because he's still dreaming up new ideas to touch the world for God and venture beyond known horizons - with all his added years of wisdom.
So really, we could be 20 and 'old' because we're not doing or dreaming up anything new.
Whatever our age by number, what matters is we're living with vision and purpose. That will keep us 'young' till Eternity beckons.
J a n i e ll e