I'll be 24, and FH will be 28 when we get married, and we'll have been together for 5 years.
Both of our parents have been divorced. My dad and his mother have not re-married, but my mother and his father have re-married (not to each other though!). My mother has been married I think 4 times now. FH and I have very similar values and life plans, and he's truly my best friend. We look at our parents and look at where they have all ended up and how they failed, and we want to use this knowledge to help us get past those issues we might come across ourselves. Failure and giving up on each other is not an option, not through what we've been through so far. We feel that we've already had our "mid-relationship crisis", our core has been absolutely shattered, but we've come out of it stronger and more united.
I don't remember the exact number of years, but without looking it up my grandparents got to 60 years married. Our bold goal is to beat it, with death being the only thing that prevents it