Question on Metabolisms

datikihut21

So I get the whole calorie deficit idea, but it doesn't really take into account the speeds of metabolisms in different people. I could eat the exact same thing as an 87-year-old man while doing no other exercise, but I'm most likely going to burn it off fast because I'm 23 and my metabolism is running faster than his. Right? I think I'm really wondering if there is any possible way to account for this somehow.