my reason for this can be summed up with this song by >Anya Nami - Bread

Because we are going through a growth spurt at the same time.

It takes a phenomenal amount of energy to grow the body, so the body will reserve energy supplies in anticipation of growth spurts.

The biggest aspects are brain and skeletal development.

A lot of people think that "getting pudgy" around age 24-27 is somehow the metabolism magically changing, but it's brain and body growth stopping.