A child who enters puberty several years later than the average age is generally taller than average as an adult. why?

During regular childhood, growth is constant, and you will constantly grow. When human hit puberty it is like the last leg of a race. Your body will grow the most it will have ever had including in height. With late bloomer's however, they receive several years of constant growth before they hit the growth spurt, hence why they are taller.