As paint ages it becomes lighter not darker. Lighter than a burn. And the cracks here should be showing through to the paper or the layer beneath. this is because as it dries over time the shrinking paint causes stretching and minor cracks where there is a difference between thick and thin paint. The dark looks like a bad fresco charred by smoke. This is on parchment or a wall?
Also I'd make the text on scrolls.
"Tiber septum victorious" on left and "heathen god surrenders" on right so that it correlates with the alignment of the 2 factions below.
Basically agreeing with ejrs and 6plus mostly.
Figure in middle should be slightly larger all secondary figures smaller. Vivec still too tall.
The emblems around the outside of frame should be more legible as well. These things were made to be seen and understood without need of words so symbols need to be bold and legible, immediately recognizable, the image more simple.
If on paper paint should be thin. Add one color at a time. One layer at a time with prob max of 2-3 layers on paper. Little or simple shading, colors not running together and covered with what looks like charcoal. If you wish to obscure the image to hide the quality of the work FADE and desaturate as you've already done.
If it's on a wall maybe add some small chips and flecks in paint. However, think the aging was fine already. The composition mostly needs adjustment, if desired. Otherwise I'd be inclined to continue to add other shiny things, finish OE quests or interiors.