My active sim aged up to young adult, and he got the 'Get Married' wish and his parents have the 'See so-and-so Get Married' wish, so I decided to have them get married while the inactive sim is still a teenager.
I have the settings on Woohooer and SP set to allow teen marriage, pregnancy, teen/adult relationships, etc. They became engaged as teenagers, and I had no problems there. I'm having some trouble with getting a teen/adult couple married.
