If you really want to know the answer, it is in chapter 2 of the book "The Evolution of Desire" by David Buss. This is the book bearamedic99 referred to earlier.
Basically, women want men with access to resources. Evolutionarily, age was one of the cues that a female could look at. We still operate on instincts bred into us thousands of years ago, and this is one of them.
According to this book, age is still a good indicator of income, with 30 yr old men making $14,000 more than 20 yr old men, and so on. Also, older men usually have more social status. This is coupled across cultures.
Additionally, physical strength peaks in men during their late 20s and early 30s, and older men have the advantage of also having more experience, making them overall better providers.
So, guys, basically we women are genetically programmed to be gold-diggers! Sorry!