Whats the chances 👶

Im a healthy 42yr old who has two boys of 20 & 21. I was on the depo contraceptive injection for 3yrs right after i had my youngest but have never used any since and i have never fell pregnant. I had blood tests done last year and everything showed up as working normal and i still have regular periods so im now wondering why am i not falling pregnant. Am i too old 😢and do i just give up