RFF, don't get me wrong, age is a huge factor, generally the earlier you start the better your peak will be.
However, you have the advantage that you will peak in your 40s, whereas anyone starting and training seriously in their 20s and 30s will be either just about holding on, or will be declining!
In terms of your weekly mileage it's very low, meaning if you build gently and gradually your times will plummet like you can't believe.
I'll always remember a really top runner hearing i did 30miles a week years back and his exact phrase was, "you've not even started training yet" 