Age, death, smoothies

[making a fruit smoothie. B is having a fit because I made it without the one ingredient that mommy always uses, which I later, through the tears, figure out is "the black stuff that she puts in". (Vanilla, of course)]

B: Mommy makes the best smoothies. She's the one in this family who knows the most because she's the oldest. 

Me: mm hmm (nodding, wholeheartedly in agreement)

B: Yeah,...she's the oldest. And she's a doctor, so she knows how to make the best smoothies. She's probly gonna be the one who dies first out of all of us. 

Me: (Trying to keep a straight face and at the same time feeling concerned, preparing for follow up questions). Really Ben?, What makes you say that?

B: well she's the oldest so she will be the first one to get to a hundred. That's really old!!

...

(I told him none of us knows when we're gonna die and that's why we should live every day as happy as we can. But I guess he knows we won't be around forever.)