What can I use to make a cow skull look weathered or older?

For fabrics and paper tea works quite well and gives a brownish-yellowy aged look. I don't know how it will work on bone but it's worth a shot. Try it first on a small spot on the inside of the skull. This way if it doesn't work or gives a weird coloration or spotting, it won't show or interfere with other methods you may try. Whatever methods you try, I suggest you first test them out on an area that won't be seen...just in case.

Stain it using tea bags, boil the tea bags and sit them on different places all over the skull. The tea will stain the bone, and the longer you keep them on the bone the darker they will get.They use this same idea on paper to make paper look old.

the tea answers are good...you could bake it in an over too..roasted bone

Tea works very well. Mix up a cup of plain tea and then you can paint this on or dab on the tea bag. Coffee also works quite well when the granules are mixed with water. Try each one on a small area inside the skull to see whcih works best. Shoe polish also works well to :)

I have used shoe polish as well. I depends on how dark you want it. You can also water down paint and brush on the wipe off and repeat until the color desired is reached.

Leave them outside for a couple of weeks