The opposite is generally true: most people tend to burn slightly fewer calories as they age, not more. Total daily calorie burn is determined to a large degree by physical activity (especially if one is really active), but weight is a big contributor as well. A heavier person will have a higher BMR (Basal Metabolic Rate), but her energy cost of movement is higher. Answer this: Which requires more energy, moving 225 lbs across a room or 150 lbs? The heavier person burns more calories for ANY movement, regardless of what it is; not just physical activity in the form of exercise, but walking, climbing stairs, getting in and out of the car or a chair….you name it.
Additionally, there is a phenomenon that occurs with increased fitness. As you become more fit, your energy cost for movement decreases over time. It is similar to getting a tune-up on your car. When it is in good working order, it runs better and gets better gas mileage (less fuel used or in the case of a fit person, calories burned). The poorly tuned car wastes fuel, or in the case of someone who’s overweight, uses more calories per event or movement.
These are the two main causes of a calorie burning discrepancy between older and younger people.