Problems with my girlfriend due to age difference, etc.?

I'm 15 years old and my girlfriend's 83, so there's sort of an age difference, and it's making our relationship sort of difficult. One thing I can't stand is I'm always horny but she never wants to have with me. Though she let me finger her a couple times, and I gave her . But I love everything about her. I love her silky white hair, her droopy , the lovely voracious veins in her legs, the stretch marks all over her body. But she's in menopause, so she never wants . And to make matters worse, I just found out she's my grandmother that I never met before. What am I supposed to do? I'm in love with her but society says it's wrong.