Why can't my cousin get fat?

Many people have different metabolism (some people could possibly get fat easily, some can't). Also you have to consider the factor of day to day activities such as running.

Different levels of metabolism (rate of which processes happening in your body) I believe there are genetic influences on that.

Or maybe your math just sucks and your cousin is actually eating a lot less than he claims and he probably does more exercise than you.

Some people have different metabolism (some people can get fat easily, some can't). Also you need to consider the factor of daily activities such as running.

That's 'cause your cousin has a higher metabolism than you do. Your metabolism is lower, so that explains why he doesn't gain weight, and you do.

Your cousin has a fast metabolism..and for you, eating more than 2000 cal and get fat? honestly i cant believe that because our body need around 2500 calories a day,especially for teenager like yourself...if you eat 1800 calories and below a day its considered under eating

Very many 14 years olds have metabolisms so fast they can not gain fat.

Fast metabolism

He probably had a very high metabolism. Or he's just very active

Metabolism differences.

He probably has a faster metabolism ( I would kill for a faster one) I keep myself thin thru lots of exercise and I try and eat as healthy as I can