Cardio is overrated unless you're doing it for, you know, the cardio benefits. In terms of calories burned/time you're frankly better off just eating less. But if you're old (like me) and have a desk job (also like me) there are health benefits outside of weight management you should be concerned with.
A lot of men gain/retain weight in their stomach, it's just the normal fat-distribution pattern for males. Commonly that means you'll gain weight there first and lose it there last. But if you're generally a skinny person but have a big belly it could be helped by a number of non-diet/weightloss-related things, like dumping carbs/losing water, or by working on your posture, or by working on gaining muscle for an overall more proportional build.