How long do you have to be married to be considered an old married couple?

It will be 7 years married in 17 days :)

33 years

You become an old married couple the first time you or your other mention to some single person how great that single person’s life will be when that single person gets married.

Maybe it’s when you reach that point in time when no one you know can imagine you not being together. You are a unit and though you may disagree at times, get on each other’s nerves at times, well, you know why you’re together and it’s not out of habit. You still love each other…..hopefully. Otherwise there is no advantage to being an “old married couple”, right?
For me and my wife it is going to be 25 years next year. Still going strong…weathered a few storms and all…

I made it to 8 years and it was already getting old

15 for us.

Maybe old couple comes about as a state of mind.