How can I artificially age paper without staining or dyeing?
Place the paper in a sealed box or plastic bag together with an open jar with a bit of ammoniac in it and leave it. The fumes will age it (works well with wood too).

Another way is to bake the paper at around 100 C (200 F). It will give you an even brown colour.

You can put some steel wool together with vinegar in a jar and leave it for a week or 2. Then apply it to the paper and let it dry. It will give a nice yellowish colour. This method also works very well for staining wood.