The Workshop might or might not be older than the Tower, but it probably wasn't in the Tower originally.
I am not saying that they weren't advanced, but according to the excerpt, all their weapons were made using the ones from outside the Tower as basis and the 13 GW are the ones who needed to modify their weapons so that they could work in Shinsoo. Maybe the Workshop members had created many things before their entrance, but no weapons.
As for the Hell Train, it was said that it was created to help Zahard and his companions train, so it was made after their entrance as well. Plus it's not a weapon.