There are a lot of great anti-aging techniques for mature skin, but the best cosmetics are still the common sense ones - wear sunscreen, drink lots of water, get plenty of restful sleep, stay active, don't smoke, eat healthy/take vitamins and try to avoid stress.
All of those are free! Well, sunscreen isn't free. But it costs less than La Mer. LOL. You can also wear a hat and sunglasses when you go out.
I agree with red that a professional brush kit makes a big difference in how your makeup looks when applied and can take years off simply by allowing you to not over-do anything - you can use a more skillful touch with excellent brushes. Sephora is nice, Origins, Too Faced and Body Shop all make wonderful brushes.
About powder, it's really all about your skin, the season/climate in question, and the powder itself. I don't think there is any one answer about ANY kind of cosmetic. That's what makes makeup fun!
