This is a brand new mesh I've made, and the settings for the UV unwrapping is only allowing me to lighten pack, follow active quads, mark and clear seems. I've done 1 model before that didn't have this issue.
What I've done so far to make this model is:
Used modifiers Mirror, Skin and Smooth by Angle
Used two cube meshes, which I've collapsed by center.
Blender can only UV unwrap real geometry, not geometry created by modifiers. Because the real geometry of your mesh has no faces, there's nothing to UV unwrap. (And, when a mesh has no faces, Blender grays out most of the UV menu, as you've seen.)
You'll need to apply the Skin modifier at a minimum, to provide some real faces. Note that if you leave the mirror modifier unapplied, Blender will only unwrap the real half the mesh, and the generated half will just copy the same UVs.
You can apply modifiers by switching to Object Mode, selecting the object with the modifier, and under the Properties > Modifier pane, selecting "Apply" in the little triangle menu for the modifier you want to apply.
Applying the modifier will make the geometry generated by the modifier into real geometry. The obvious downside is that there's no real way to "unapply" a modifier, so you have to be pretty committed to having the modifier applied before you do this.
