One of the awesome things about jogging and running is that you only have to worry about one competitor, yourself. A good speed is one that you're satisfied with.

Here is the Army standards tables(http://usmilitary.about.com/od/army/a/afpt.htm). Based on my age 47, I'd need to do a 9 minute, 45 second mile for two miles to pass.

Quoting the other guys and agreeing...whatever you are comfortable at that allows you to get your heart rate to a decent place. Also, what are your goals? Increased time/distance? A 5k? Marathon? Before my knees gave out, I trained at 10-11 minute miles. Believe me, it was gradual; run 45 seconds, walk 15, etc. After a few months, took a chance and ran a 5k, and was hooked. Did that for a couple of years, then moved up to an 8k (Shamrock Shuffle in Chicago). Got so full of myself that I ran the Chicago Marathon in '03 and '04, and the half in '07. Unfortunately, I didn't train properly for the '04 marathon, and I paid the price with my knees. The half-marathon in '07 was an effort to see if I could come back, but that didn't work out so well. My advice - listen to your body, and listen to professional runners on training tips and techniques (do as I say, not as I did!). Good luck!

I think at 30 you should be able to reach a 9 minute mile in short order if you really take up running. I'd do 3 miles and slowly increase the pace as it becomes comfortable--and it will. Key thing is to be gradual, injuries really screw things up. Run/walk mix is ok until you get in better shape. When I moved from 3 mile runs to 6 it sort of opened up the gate to faster and longer (including a marathon) because you get runner's high and just cruise.