Her blond hair and her frequent laughter gave an impression of extreme youthfulness.

From a twenty-first-century perspective the two men's most striking joint feature was their extreme youthfulness.

I profess to be a steady, level-headed, prosaic sort of person, and this surprising reversion to extreme youthfulness rather staggered me.

Although he was upwards of forty years of age when he left Canada he had always retained an appearance of extreme youthfulness.

Johnny's clumsy attempt to depreciate what he wanted very much to buy merely convinced Tomaso's brother of the extreme youthfulness of Johnny.