Unboyish

The emerald-green bathing suit pulled taut across boyish hips and decidedly unboyish breasts, the wet material leaving little to the imagination[…]

Everybody knew that had he properly exerted his abilities he was capable of beating almost any boy; so, to quiet his conscience, he professed to ridicule diligence as an unboyish piece of muffishness, and was never slow to sneer at the "grinders," as he contemptuously called all those who laid themselves out to win school distinctions.