This is an idea I've come across before and don't totally understand. How can you plan when you want to get married before you meet the person you want to marry? Trying to timetable True Love like something that can only lead to bad and sad places.
If your in a relationship where you don't plan to marry that person, then there's the answer. "I don't plan to marry you or have children, possibly ever. Though I'm human and things change." Which is basically what I said to my husband when he started talking about marrage 6 months into our relation ship. And I was human, and things did change. I gave him the respect of being honest with him at the time, and honest with him when things do change.
I guess the obvious disparity is that for ladies, our baby making abilities are on a definite time table. If having a kid with your DNA is on your life's to do list, like it or not, there a time table involved. If a partner's goals are to one day ideally marry and have children, as in Dan's case, saying "I'm not looking to get married for X number of years, or have children until I'm X years old or have completed X goal" doesn't mean committing to doing such a thing with the current partner. This serves to lay the cards on the table, which is part of respectful, honest communication. It sets the potential shelf-life of the relationship for the other person, telling him or her they need to either be on board with the same plan or understand his or her partner's path is likely to diverge from his or her own at a certain point. This doesn't mean things are fixed or anything, but it's about communicating trajectories. If either partner isn't honest or open about such things, you could end up really unhappily in love with someone who wants something you have no desire for. I've had two close friends end loving partnerships for such reasons recently, and it's god awful to love someone dearly and want very different things out of life.
In Dan's example, he wants to have a wife and kids one day, so the important question becomes, how long would he be willing to wait for his current lady to come around to such a plan, or if she never wants to marry, would he be okay with that over the long term, short term, etc?
A lot of people are really frightened about talking openly and honestly about the "big things." I don't know why, but I do think it's why so many people end up divorced these days. I really do think telling the truth is one of the most important things to share with a partner, in all manners. It's hella hard work, and scary, but so damn worth it.