Wallace beat 18-year-old Marc Bourgeois 5 and 3 in the 36-hole final at Beaconsfield.
Wallace is three years younger than Donald Carrick, who was 18 when he won in 1925. The teenager won six matches this week, including a victory over defending champion Richard Scott in the semifinals.
Tiger Woods was 18 in 1994 when he became the youngest U.S. Amateur champion.
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