If you're not looking to stray very far from the styling of the boat shoe, but still want to look age-appropriate, the camp moc is perfect. A very close relative of the boat shoe, the camp moc even has the same wraparound leather lacing and general profile.
However, the front lacing sets it apart with a distinctive row of metal eyelets.
L.L. Bean's Camp Moc ($89) is a wonderful example of this kind of shoe.