Do you think it's bound to fail if the woman is older than the man in the relationship ?

No. I met my lover 40 years ago. She was 43 then and I was 8 years younger. Do the math! and 40 years later she is still exciting, stimulating and vibrant

I feel that way or have those doubts as my bf is 5 years younger.. but in reality i know so many couples where the woman is older and they are doing just fine. eg my mother is 10 years older than her husband and I know they will be together for the rest of their lives

Not at all, age is just a number...but it really depends on the spread in the ages. Maybe plus or minus 10 years is okay after that it can get creepy.

No, my parents have been married 40 years and mum's older than dad.

no