I've been married 13 years and we are only in our late 30's.
I met my wife in college when I was 18 and she was 19. On October 14th of this year I will have been dating or married to my wife for 18 of my 36 years. We were just talking the other day about the fact that I am now at a point where I have known my wife for over half of my life. Seems odd to me (in a good way).
And like others have already stated, the only question is how and why my wife has put up with me for so long.