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youthful; young; young-looking
祖母は八十歳だが若々しくて元気いっぱいだ。
My grandmother is 80 but youthful and full of energy.
運動を続けると若々しさを保てると言われている。
It's said that continuing to exercise keeps you youthful.
彼女の若々しい笑顔は周りを明るくするものだ。
Her youthful smile brightens up those around her.