If all you want to do is flatten the shiny paint to look "old"
Mask the canopy off, then give the whole plane a "mist" coat
of gray paint that is highly thinned, and sprayed at a higher than normal pressure. This in itself will make the paint seem aged.

And /or get a plastic model of the subject so you can locate
panel lines etc,then lightly draw them on the plane with a
pencil . Get some drafting tape and some graphite.

Always keep in mind how the air flows over the airframe.

Put the tape on the leading edge of the pencil mark.
Very carefully .place a small amount of graphite on the
tape in several locations. Use a cotton ball and lightly
drag the graphite off the tape onto the surface. This will
produce a shadow effect. With some practice this can be made
to work well . I strongly advise that you don't try this for
the 1st time on your new scale model . Get the technique
worked out on a test plane . When your happy with the
results then do your front line model .

This should at least get you started


Best regards,
good luck

Roby