"proposition de mariage" should also be accepted.
"proposition" sounds like something professional.
perhaps, but google "proposition de mariage" and see how many hits you get- not to mention quite a few youtube videos of people proposing. I think that show it's in common use.
Let's say it is less elegant than "demande en mariage" in the French culture.
pourquoi "jeune." L'homme est masculin
"jeune" is the masculine and feminine, (singular) form.
Couldn't be "demande de mariage"?
the way the English sentence is formulated seems so bussiness like. I see him using a flipchart