I would ask you use an alias for me.

Six-hundred fifty, give or take a decade. [They did keep accurate records; it's a Long Story why he has that much error on his age.] I have been undead for the better part of four years.

Yes, though they may not work very well in many cases. It varies by ingredient.

Can you share what it is you are planning? [A pause.] This is curiosity, not a prelude for an objection.