The Young Plan did pass. And does pass in this game too. You're confusing it with the referendum which was held to denounce the Young Plan. Which got 14.9% of the voters partaking in it.
In the game, if you have the foreign ministry, you can suspend the reparations. It is guaranteed if you notify the foreign powers that the right wing parties are attempting to remilitarize the German military. The right wing parties hate you for it though.