Assuming that you installed your game in its default directory, the game should be installed in:

C:\Program Files\Microsoft Games\Age of Mythology

You should also have a shortcut to your desktop.

Right click the shortcut file --> Go to properties
You should see a target field that would probably have something like "C:\Program Files\Microsoft Games\Age of Mythology\aom.exe"
You need to change this target to:
"C:\Program Files\Microsoft Games\Age of Mythology\aom.exe" xres=640 +noSound +noIntroCinematics bpp=16 +window +lowend +terrainHalfDensity +lowPoly -waterbump skipMipMapLevels=1 graphicDetail=2

Once that is done, launch the game offline and manually adjust your resolution to your desktop supported resolution and it should work fine thereafter.

EDIT:

Don't forget to change the game path in target to whatever path you installed your game in. The part that I have highlighted in bold must match your installation path.