Well, I am 25, and I have been running for a while now. I am not an expert, and it still takes me about 25 minutes to run a mile, on the treadmill.
So i think you should start slow. Do about 5 to 10 miles a week.
Are you looking to lose weight, only by running?
Are you following any exercise program? Can you run a 5K? If you can't run far, check out the "couch to 5K" running plan, and see if it's what you're looking for.
Started C25K 2/14/10 Age 51 and NEVER have run before.
Coventry Challenge 5K 3/20/10, end of W5 of C25K. 40:44
Spring Forward 5K (YMCA) 4/10/10 39:57
Focus 5K Run/Walk 5/13/10 32:24... in Orlando on a totally flat course
Coventry Challenge 5K 3/19/11 37:59
?Operation Backpack 5K 5/21/11 ??? fast-paced race, finished next to last
Coventry Challenge 5K 3/17/12 38:11
I highly recommend the C25K program!! It got me started in February and now I run 3 miles. If you've got an iPhone or iPod Touch, you can download a few different apps. Here's the one I love the most.