do not increase mileage more than 10% a week build up the mileage gradually
at middle age, listen to your body....if the body says "no", then stop and rest
whatever run/rest model you choose is dependent on how you cope but bear in mind the endurance build up at each run lasts only about 3-4 days before is diminishes....to maintain the same endurance, you need to do the same within the 3-4 days to MAINTAIN only. If you want to improve, then you need to push the 10% increase within the 3-4 days...its like climbing the stairs....increase/maintain/increase/maintain.....try a bit and find a comfortable rhythm
don't just focus on running....you need to do some cross training also..