Excluding rare and serious metabolic conditions, which should be diagnosed by a doctor, people's metabolisms tend to be within 200-300 calories of each other. This examine.com meta-analysis explains this in greater detail.
They conclude that:
Metabolic rate does vary, and technically there could be large variance. However, statistically speaking it is unlikely the variance would apply to you. The majority of the population exists in a range of 200-300kcal from each other and do not possess hugely different metabolic rates.
This review of 67 scientific studies found that:
"when adjusted for differences in fat-free mass, resting energy expenditure values in obese and nonobese individuals tend to be comparable"
and there is
"no association of baseline resting energy expenditure with weight change among 775 men during a 10-year period".
The review draws the conclusion that:
"Regarding metabolic factors, available data indicate that although there are variations in resting energy expenditure and in the thermic effect of food, there is little evidence that these variations contribute significantly to the observed trends in weight gain."