1. Prepare the glaze: In a small saucepan, bring balsamic vinegar to a boil over medium heat. Cook until vinegar is reduced by half and thickens slightly. Add lemon juice, almond extract, and agave, stirring to combine. Remove from heat and set aside.
2. Preheat grill to medium-high.
3. Coat each peach half with olive oil and place on the grill cut side down; cook for 3 or 4 minutes each side, just until grill marks appear.
4. Remove peaches from the grill and place face up on a dessert dish.
5. Drizzle with balsamic glaze, garnish with mint sprig and serve immediately.