My teen girl had an amorous date with the expected results. It's been a pain getting them together, since he has an after school job and as soon as they start interacting, he takes off to work. When he gets off, it is too late. I was trying to get them married, but I couldn't keep them together long enough (I just started, but I've gone through this before). When the option "Move In" came up, I took it. Then they can get married at their leisure. They both have 'Get Married' and 'Marry ---' wishes for 5,000 happiness points each. On his first day at school, he got the "Cultural Interview" opportunity. She already had it. So they went to France. I should have married them before they left, but her birthday is coming up. I can delete his other wishes like "Jam With Another Sim", but her other two are worth another 5,000 happiness points. I hate missing the smaller wishes for her, such as 'Meet a Local', 'Eat Frog's Legs' or 'Visit a Museum'. So I decided to have them get married in France and open up those wish slots. I CAN'T!!

I'm sure any response will be too late, but it may help somebody else (or me later). At least I'll know what I should have done.

Are they engaged yet or still earlier in their relationship progression?

On City Hall (or in France, the map tag of the Base Camp which is the assigned substitute) or an in-game computer, NRaas > Woohooer > General > Debugging > True. This should reveal all Romantic commands on sims and other objects with the ones inaccessible greyed out. If you hover your mouse over a command that is blocked, a tool-tip should pop up with the reason. What does it say for the command, whether it's Get Engaged/Propose or Get Married, that is blocked?

Be sure to switch Debugging back to False before resuming gameplay as the function generates tons of complicated log files on the entire world being played that no one needs to see for this purpose, and that can drag performance down.

It'll be a bit before they get back together. They spent most of the first day trying to get married. One just went to sleep below the Museum and the other just woke up under the burial mound. Once they finish I'll try again.

Ok, they are together now. "Propose Marriage" is greyed out, the reason being "Teen Denied". They have been going steady for a while, with maxed out relationship, but haven't proposed yet.

Okay, under EA standard there is no teen marriage allowed so they are being blocked from becoming fiances for this reason. Woohooer has a bunch of settings that unlock teen woohoo, teen/older romance, risky, try for baby, etc. But for marriage, I think what is holding you back might be StoryProgression settings. Are you using NRaas StoryProgression?

NRaas > SP > General Options > Options: Romance > Allow Teen Only On Pregnancy > (default is True)
When enabled, teens are only allowed to get married when one of them is pregnant

You will also need to check the Caste Options for the Teenager caste (or the Sim Options for these two sims in particular) to ensure these sims have Romance: Allow Steady and Romance: Allow Marriage set to True on them.

If that's not it, I'm going to have to ask my colleagues here which setting I am not remembering properly at the moment.