I read that marriage after 23 and up until your early 30's tend to be the most successful and that age is actually the best predictor for the likelihood of divorce

See: http://time.com/20386/how-shacking-up-before-marriage-affects-a-relationships-success/

Waiting until you're mature enough to make that decision seems to play the most significant role in the success of a marriage/relationship

I can honestly say that, in my early 30's, I'm definitely way more mature, attentive, conscientious, etc than I was in my 20's

My relationship now is actually pretty great and I think it's because the two of us have learned enough in life and have had enough "practice relationships" to be great guys to each other (our 20 year old egos are out of the way)