Possible Clues:

• Physically fit
• Island retreats predicted to keep one healthy
• Robust, skilful lad losing energy finally perished
• Strapping appropriate to the sailor type?
• Clever chap that's died like a naval rating
• Hale and hearty
• Fit
• Not physically unfit
• Strong and healthy like one who is at sea
• Fit first victim, say, when box office expired