noun which may take the genitive case particle 'no'
young and energetic; youthful and promising
Literary expression describing a young person full of vigor and potential. Mostly found in formal writing or classical contexts.
He is expected to do well as a young and promising man.
前途有望 is more common and means 'promising future', while 少壮有為 emphasizes youth and energy.
A yojijukugo (four-character idiom) combining 少壮 (young and vigorous) and 有為 (capable, promising). The exact historical origin is uncertain.