I didn't get married until my mid 30's because I hadn't met the right person and wasn't willing to compromise. That was me.
My best friend got married in college to the right person and they are in the same boat my wife and I find ourselves: Pleased and delighted we have shared our lives so far and are willing to share more: Great kids and happy in our struggles past and present.
The one trait I think all successful relationships share is "work through it" communication: I'd like to meet the couple that never argues so I can rub their unicorn horn for luck.
Maturity is best expressed in a relationship when the common good gains purchase. It isn't easy.
The whole thing could blow up tomorrow, btw, and I could be sleeping on CP's couch writing my own Anti-Marriage Manifesto - forward written by PoP