Age, sex, and weight impact the probability of someone being able to exert 200 watts for an extended period.
But, 200 watts for an hour burns about the same calories for all of us, ignoring efficiency which varies a little from person to person.
200 watts x 3600 seconds/hr is roughly 720 kilo joules and is roughly how many calories one would burn at 200 watts for an hour, irrespective of weight, sex, and age.