"You don't have to worry about age. I'm an elf I will live more than 300 years and my appearance won't change."
1.) I don't think YOUR age is the concern here.
2.) Put a ring on her finger and sheath your meatsword inside of her until you die of old age, already.
It's nice to see characters actually figure out that a protagonist is a special existence and then directly confront them about it. While it's not rare for them to figure it out I feel like they usually just let it slide.