Interesting question.
I suppose for one it would depend on what sort of illusion it was. If it was mind-affecting, then people would basically see what they expected too. If they saw an aged wall, then they would see the illusory part of it as being aged also.
Other kinds of illusions though, that manipulate light rather than play mind tricks, probably wouldn't update themselves. Its just not in their spell descriptions. It probably isnt a big deal though, since a wall would have to be pretty old and/or dirty before it mattered enough to make a difference. And even then, the caster could just let the room age (or scatter some dust about to make it look old and dirty) and then lay down an illusion of a matching section of the wall.
In short...no, the illusion wouldnt age.
