How did I go from pear shaped to apple shaped?

I am a 43 year old male who basically is apple shaped (big belly, no butt, thin legs). However, as a teenager, I was pear shaped with a flatter stomach heavier legs, and kind of big butt. I also know many other guys my age who are top heavy now but were also bottom heavy as teenagers. How does this happen? Does the weight shift as one gets older?