Hey, I'm over 35, so I need to know about this stuff too. Apparently something like 8% of men at 40 years old have some level of BPH. In another ten years it goes to 40% or so.
Although you don't have BPH, or prostate cancer, there is nothing wrong with taking supplements that are used to treat them as a preventative measure.
Basically, there are a bunch of supplements that interfere with inflammation of the prostate, conversion of testosterone to DHT, induce cell apoptosis, inhibit metastasis, reduce free radical damage and so on.
If you are researching, read up on recent studies concerning:
The LEF ( http://www.lef.org/ ) is a great place to find out about issues relating to aging, such as BPH or cancer. However, I do find them a bit quick to go from studies in mice to offering supplements.
If you have a serious condition, such as cancer, of course you don't mind making the leap and trying any idea because you really need to find something that will help, but if you are just looking for preventatives, you'll want results from clinical trials and developed mechanisms of action.
I currently have two older relatives with fairly serious prostate conditions. Look into it and see what you can do... it's basically an epidemic and it can probably be greatly reduced with supplementation.