It's just a thought but wouldn't your friends 12 year advantage allow him to exercise more vigorously than yourself thus canceling out any advantage you may have. I weightlift and run most days and am not so sure that being heavier means you'll lose body fat quicker. If you(no offence) can't stay away from the carbs and the junk food and you don't train hard and your friend does then even though he has less body fat he will lose more than you, it's all a question of discipline.
I think the age difference cancels out any advantage either of you think you may have.
