What-

ma'am, we need the skincare routine, please ~~

At least 50, but I'm guessing closer to 65-70. Because Riesel said something about her holding onto revenge for "50 years" and people aren't born with a desire for revenge. Lol

wait 50yrs have passed since she held onto her wrath
so when she was proposed 2 she had 2 be at least 15 (according 2 general isekai adult age)
so she has 2 be at least 65