youthful

英 ['juːθfʊl; -f(ə)l] 美['juθfl]

But over the next few decades labour forces in rich countries are set to shrink so much that inflows of immigrants would have to increase enormously to compensate: to at least twice their current size in western Europe's most youthful countries, and three times in the older ones.

Of course, youthful idealism is often courageous, and no one likes to give up dreams.