After 25 for sure, but more importantly, I would like them to live on their own for a while without the worry of having to "deal" with another person's emotions, habits, input, involvement, etc. I want them to have a time in their life where the only person they have to worry about are themselves. I met DH at age 14 and we have been together ever since. I don't regret it for a minute - my life circumstances and his were optimal for the path we have walked - but our kids have been raised very differently than we were, and I think for the good of themselves and whatever future marriage they might have, it would be very beneficial for them to have a few years of independence.
DS17 refuses to have a girlfriend in high school because he sees his friends bogged down with teen girl angst and he doesn't want, or have time, to deal with it, plus he is adament about moving back to our home state for college/career and says he doesnt want to risk marrying someone from here who will eventually want to stay in this area, haha. Smart kid!! He keeps all girls strictly in the friend zone, lol, and says he sends them back to their boyfriends when they start to get dramatic
DD12 says she doesn't want to get married at all....she has a ton of friends that are boys but doesn't really like people touching her lol, so boyfriends are out for now. I feel for her future husband....
DS11 will be the one with all of the girls and their drama, I just know it. Theres already a few 5th grade girls who "like" him and he is being well trained by his big sister on how to deal with crazy women. He will probably be the one to marry at age 25. Haha