"we're getting old, mommy"

Tonight while he was going to bed, David told me his legs were getting old. Here is the rest of the conversation...

D: "We're getting old, mommy"

M: "Really dude, why are we getting old?"

D: "We drink too much."

Me to myself: Really? Where is he going with this? Am I up for whatever it coming?

Me to him: "What are we drinking that is making us old?"

D: "Mommy, we are drinking too much water and that is making us too old. And too much juice too. It's making our legs old".