I think being sad can last for a couple of minutes/ hours
But being depressed can last for days/months/years.. makes you shut out of the world, makes you uninterested in things, makes you have suicidal thoughts and other stuffs.
They’re both similar..(my opinion)
Well as you grow older, your body adapts and adjusts for you to survive as well. Your mind or brain becomes a bit bigger than before, only up to the capacity of your skull. You gain and retain or forget experiences that will be beneficial and not beneficial to you. Your body, from head to toe will grow as well. From your bones, to your muscles, to the hairs that will grow from top to bottom and many more changes.
Hope its right!!! :)