Are some women more fertile than others? I mean two women with no fertility issues.. can one be more fertile than the other?

I ask this because my sister is on her 6th month TTC with no fertility issues and I have been pregnant 6 times and taken this long:
1st 7 months
2nd second go
3 first go
4th first go
5th second go
6th first go
What I'm trying to ask is for the people that have no fertility issues and take say 1/2 years to conceive are they just as fertile as say me or other women who fall pregnant fast and it's just down to luck? 
I sound so thick I apologise x

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