Youthful/ˈjuːθfl/ Definition 1 of 3Pro Tip 1/3Age Neutral Can describe someone older with young energy, not just the young. The grandmother's youthful zest surprised everyone at the reunion. Pro Tip 2/3Positive Energy Often signals positivity and liveliness in character or actions. His youthful enthusiasm made the team more optimistic. Pro Tip 3/3Not Naive 'Youthful' implies vigor, but not necessarily inexperience or naivety. Her youthful energy was an asset, even with her decade of experience.