5 miles three times a week is a good start.
There is no magic number to how much you should be doing to lose weight. You have to find the magic number for your metabolism. Remember, as we age our bodies dont' shed the weight like they used to. So, be patient it will come off, but it may take longer than before. I know this not the answer you were looking for.
Something you should keep in mind is that you should never increase your mileage per week by greater than 20%. So,
if you decide to start upping the mileage then take it slow and let your body adjust to the changes. Increasing your weekly mileage by greater than 20% will make you more prone to injury and fatigue.
If you are training for a distance run there are great guides on the internet on how to structure your weekly runs, how many weeks you should train for a particular distance and how to increase your mileage.
Run on my friend!!!!