I got married at 18, after being together since I was 14 and knowing him since I was in gradeschool. I think it depends on the majurity and understanding of the couple themselves. Hubby and I have overcome a lot, but its only made us stronger. We have now been married 8 yrs and together 12 yrs and I am pretty sure nothing aside from God can seperate us! But we took the commitment very seriously!
Doomed? No. I was married at 19 and we're still together after 12 years of marriage and 16 together. I will say that statistically the marriage is more likely to fail and you'll probably have a lot of extra challenges. But it's not doomed.
I was married at 22. and he 21. We're now pushing 15 years of marriage. It hasn't always been roses and unicorns but we are still going strong! I think any marriage can fail if the partners in the marriage want it too.
I don't think so, but I think there are a great many who don't 100% know what it takes to hold a marriage together. There is also a great amount of growing up and changing during early adult life for so many and so many grow apart. I've been married for only 2 years and married a few days before my 22nd birthday.