I'm 16 and a guy how do you lose lower back fat?

Lose weight: Unfortunately, there are not really any tricks or special exercises to lose fat in particular areas. You need to lose weight overall, then you'll see an improvement in these areas. Diet and exercise - it's more important to make small changes that you can live with long term than to lose a lot of weight (only to gain it back). Meeting with a dietician is often helpful. Best of luck!