As we age, we lose muscle. We lose 15% a decade after 50 and 20% a decade after 60. Body builders have always known the importance of casein for creating lean muscle mass. Why use casein verses whey? What is it? It is what mostly makes up milk. Milk is 80% casein and 20% whey.
The reason whey is used by so many for a pre work out drink is because it is rapidly absorbed by the muscles in 10 minutes so when you work out, your body is done digesting. It is also so good right after a workout because it will rapidly refuel the muscles which are made of protein.
Casein is better for a protein to use right before bed because it is a slowly digesting protein that will refuel our muscles all night long. If you prefer, just eat Greek yogurt or cottage cheese or yes even warm milk to do the same thing.