What is the appropriate attire for a middle-age women at a 5 pm wedding and a 6 p.m. reception?

I think a tasteful cocktail dress would be appropriate.

Edit

My 50 year old aunt just worse a satin wrap blouse with well tailored black trousers to a 5pm wedding last weekend. She looked gorgeous and appropriate She paired it with gold kitten heel shoes (her wrap blouse was goldy colored) and pretty gold jewelry.

If you'd like to try new things:
This asian style formal dress is often adapted for middle aged women in big celebrations including wedding;)
The dress is usually very conservative, so that might suit you.:)
http://www.bitablue.com/images/HH260112.jpg

That's very pretty, NiceSpringGirl :)

I think slightly darker colors and a below the knee skirt or dress slacks would be fine.