Here is a little recapitulative of the most common techniques I and many other prop-makers uses for ageing paper, books, cardboard, etc.
First, for the ones who wants to make fake newspapers or news clippings a good idea is to use newsprint blank paper which is sold in art material shops because white printer sheets just don’t have the feel of newspaper (too heavy). But when printing them you should be careful with the printer because newsprint is a fragile paper so you can temporary tape it to a common sheet of paper.
Also , for light ageing of your paper props you can distress them a little bit by folding them a couple of times or sanding them with fine sandpaper, this will make them looks like they have been handled a couple of times before, but they will still looks quite recent.
After that the next method involves some liquids the classics are: tea, coffee and diluted ink crystals. For this method you can either immerse you paper in a solution of the thing, or brush it on with a cloth or a brush. For an even finish with only little splatters and heavy stains, let it dry at air. For an more worn out and dirty/stained look, put in a pan in your oven (electric) at 200 Fahrenheit for a couple of minutes. For tea and coffee, use new one and make a really strong infusion to have a more noticeable color. Note that it will erase some kinds of ink like the lines on lined paper.
Another technique is to put the paper directly inside the oven, on a pan and bake it, with this method you will have an really even browning of the paper, good for an clean aged effect, take care not to overlap paper sheets because they will leave traces on the sheets underneath. And also put your oven at the same degree mentioned before (200 Fahrenheit) and watch it while it bakes.
Finally there is a fourth technique to make paperlook really old, which is oxidation, the same process that papershould normally follow as it ages. It takes only two products steel wool (fine) and vinegar. First put a lot of steel wool in a sealed container (glass work fine) with vinegar over it. Second, let the vinegar fully dissolve the steel wool (can take between one to four weeks so be patient) in the closed jar. And finally apply evenly on your paper prop with a brush or a cloth and wait for the paperto oxidize, it would take only a couple of minutes, applying only the oxidant on paper will give it an really yellowish tint which simulates well old paper. You could also put some tea before, let it dry or cook it, and apply the oxidant after. This alternative way will give a grayish tint, which will looks more like newspaper. Allow to dry at air. This technique also work on (dry) wood, but before applying the oxidant, paint some strong tea on all the surface you want to age and let dry. Once it has dried apply the oxidant, and watch your wood piece becoming grey and old-looking in minutes.